View source for Supernova

{{Short description|Astrophysical phenomenon}}
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{{Use dmy dates|date=February 2023}}
[[File:SN1994D.jpg|thumb|right|upright=1.3|[[SN 1994D]] (bright spot on the lower left), a [[Type Ia supernova]] within its host galaxy, [[NGC 4526]]]]
A '''supernova''' ({{plural form}}: '''supernovae''') is a powerful and luminous [[explosion]] of a [[star]]. A supernova occurs during the last [[stellar evolution|evolutionary stages]] of a [[massive star]], or when a [[white dwarf]] is triggered into runaway [[nuclear fusion]]. The original object, called the ''progenitor'', either collapses to a [[neutron star]] or [[black hole]], or is completely destroyed to form a [[diffuse nebula]]. The peak optical [[luminosity]] of a supernova can be comparable to that of an entire [[galaxy]] before fading over several weeks or months.

The last supernova directly observed in the [[Milky Way]] was [[Kepler's Supernova]] in 1604, appearing not long after [[Tycho's Supernova]] in 1572, both of which were visible to the [[naked eye]].  Observations of recent [[supernova remnant]]s within the Milky Way, coupled with studies of supernovae in other galaxies, suggest that these powerful stellar explosions occur in our galaxy approximately three times per century on average.  A supernova in the Milky Way would almost certainly be observable through modern astronomical telescopes. The most recent naked-eye supernova was [[SN 1987A]], which was the explosion of a [[blue supergiant star]] in the [[Large Magellanic Cloud]], a [[satellite galaxy]] of the Milky Way in 1987.

Theoretical studies indicate that most supernovae are triggered by one of two basic mechanisms: the sudden re-ignition of nuclear fusion in a [[white dwarf]], or the sudden [[gravitational collapse]] of a massive star's [[stellar core|core]].
* In the re-ignition of a white dwarf, the object's temperature is raised enough to trigger [[Thermal runaway|runaway]] nuclear fusion, completely disrupting the star. Possible causes are an accumulation of material from a [[Binary star|binary companion]] through [[Accretion (astrophysics)|accretion]], or by a [[stellar merger]].
* In the case of a massive star's sudden implosion, the core of a [[stellar evolution#Massive stars|massive star]] will undergo sudden collapse once it is unable to produce sufficient energy from fusion to counteract the star's own gravity, which must happen once the star begins [[alpha process|fusing iron]], but may happen during an earlier stage of [[metallicity|metal]] fusion.

Supernovae can expel several [[solar mass]]es of material at speeds up to several percent of the [[speed of light]]. This drives an expanding [[shock wave]] into the surrounding [[interstellar medium]], sweeping up an expanding shell of gas and dust observed as a supernova remnant. Supernovae are a major source of [[chemical element|elements]] in the interstellar medium from [[oxygen]] to [[rubidium]]. The expanding shock waves of supernovae can trigger the [[star formation|formation of new stars]]. Supernovae are a major source of [[cosmic ray]]s. They might also produce [[gravitational wave]]s.

== Etymology ==
The word ''supernova'' has the [[plural]] form ''supernovae'' ({{IPAc-en|-|v|iː}}) or ''supernovas'' and is often abbreviated as SN or SNe. It is derived from the [[Latin language|Latin]] word {{lang|la|[[nova]]}}, meaning {{gloss|new}}, which refers to what appears to be a temporary new bright star. Adding the prefix "super-" distinguishes supernovae from ordinary novae, which are far less luminous. The word ''supernova'' was coined by [[Walter Baade]] and [[Fritz Zwicky]], who began using it in astrophysics lectures in 1931.<ref>{{Cite journal |last=Zwicky |first=Fritz |date=1 January 1940 |title=Types of Novae |url=https://link.aps.org/doi/10.1103/RevModPhys.12.66 |journal=Reviews of Modern Physics |language=en |volume=12 |issue=1 |pages=66–85 |bibcode=1940RvMP...12...66Z |doi=10.1103/RevModPhys.12.66 |issn=0034-6861}}</ref><ref name=":1">{{Cite journal |last=Osterbrock |first=D. E. |date=2001-12-01 |title=Who Really Coined the Word Supernova? Who First Predicted Neutron Stars? |journal=American Astronomical Society Meeting Abstracts |url=https://ui.adsabs.harvard.edu/abs/2001AAS...199.1501O |volume=199 |pages=15.01|bibcode=2001AAS...199.1501O }}</ref> Its first use in a journal article came the following year in a publication by [[Knut Lundmark]], who may have coined it independently.<ref name=":1" /><ref>{{Cite OED|supernova|id=194435}}</ref>

==Observation history==
{{Main|History of supernova observation}}
Compared to a star's entire history, the visual appearance of a supernova is very brief, sometimes spanning several months, so that the chances of observing one with the naked eye are roughly once in a lifetime. Only a tiny fraction of the 100&nbsp;[[billion]] stars in a typical [[galaxy]] have the capacity to become a supernova, the ability being restricted to those having high mass and those in rare kinds of [[binary star system]]s with at least one [[white dwarf]].<ref>
{{Cite book |last1=Murdin |first1=P. |url=https://archive.org/details/supernovae00murd/page/1 |title=Supernovae |last2=Murdin |first2=L. |publisher=Press Syndicate of the University of Cambridge |year=1978 |isbn=978-0-521-30038-4 |location=New York, New York |pages=[https://archive.org/details/supernovae00murd/page/1 1–3] |language=en}}</ref>

===Early discoveries===
The earliest record of a possible supernova, known as HB9, was likely viewed by an unknown prehistoric people of the [[Indian subcontinent]] and recorded on a rock carving in the [[Burzahom archaeological site|Burzahama]] region of [[Kashmir]], dated to {{val|4500|1000|ul=BC}}.<ref name="Joglekar">{{cite journal |last1=Joglekar |first1=H. |last2=Vahia |first2=M. N. |last3=Sule |first3=A. |date=2011 |title=Oldest sky-chart with Supernova record (in Kashmir) |url=http://www.tifr.res.in/~archaeo/papers/Prehistoric%20astronomy/Oldest%20Supernova%20record%20in%20Kashmir.pdf |url-status=live |journal=Purātattva: Journal of the Indian Archaeological Society |issue=41 |pages=207–211 |archive-url=https://web.archive.org/web/20190510190932/http://www.tifr.res.in/~archaeo/papers/Prehistoric%20astronomy/Oldest%20Supernova%20record%20in%20Kashmir.pdf |archive-date=10 May 2019 |access-date=29 May 2019}}</ref> Later, [[SN 185]] was documented by [[Chinese astronomy|Chinese astronomers]] in 185 AD. The brightest recorded supernova was [[SN 1006]], which was observed in AD 1006 in the constellation of [[Lupus (constellation)|Lupus]]. This event was described by observers in China, Japan, Iraq, Egypt and Europe.<ref name="Murdin">
{{cite book |last1=Murdin |first1=Paul |url=https://archive.org/details/supernovae00murd |title=Supernovae |last2=Murdin |first2=Lesley |date=1985 |publisher=[[Cambridge University Press]] |isbn=978-0-521-30038-4 |pages=[https://archive.org/details/supernovae00murd/page/14 14]–16 |url-access=registration}}</ref><ref>
{{cite book |last=Burnham |first=Robert Jr. |title=The Celestial handbook |title-link=Celestial handbook |publisher=Dover |year=1978 |pages=[https://archive.org/details/burnhamscelestia02burn/page/1117 1117–1122] |author-link=Robert Burnham Jr.}}</ref><ref name="winkler">
{{cite journal |last1=Winkler |first1=P. F. |last2=Gupta |first2=G. |last3=Long |first3=K. S. |year=2003 |title=The SN 1006 Remnant: Optical Proper Motions, Deep Imaging, Distance, and Brightness at Maximum |journal=[[Astrophysical Journal]] |volume=585 |issue=1 |pages=324–335 |arxiv=astro-ph/0208415 |bibcode=2003ApJ...585..324W |doi=10.1086/345985 |s2cid=1626564}}</ref> The widely observed supernova [[SN 1054]] produced the [[Crab Nebula]].<ref name=":0">{{cite book|url=https://openstax.org/books/astronomy-2e/pages/23-3-supernova-observations |title=Astronomy 2e |last=Fraknoi |first=Andrew |display-authors=etal |publisher=OpenStax |year=2022 |isbn=978-1-951-69350-3 |page=767}}</ref>

Supernovae [[SN 1572]] and [[SN 1604]], the latest Milky Way supernovae to be observed with the naked eye, had a notable influence on the development of astronomy in [[Europe]] because they were used to argue against the [[Aristotle|Aristotelian]] idea that the universe beyond the Moon and planets was static and unchanging.<ref>
{{cite conference |last1=Clark |first1=D. H. |last2=Stephenson |first2=F. R. |date=1982 |title=The Historical Supernovae |location=Dordrecht |publisher=[[D. Reidel]] |pages=355–370 |bibcode=1982ASIC...90..355C |book-title=Supernovae: A survey of current research; Proceedings of the Advanced Study Institute, Cambridge, England, 29 June – 10 July 1981}}</ref> [[Johannes Kepler]] began observing SN 1604 at its peak on 17 October 1604, and continued to make estimates of its brightness until it faded from naked eye view a year later.<ref name="kepler">
{{cite journal |last1=Baade |first1=W. |year=1943 |title=No. 675. Nova Ophiuchi of 1604 as a supernova |journal=Contributions from the Mount Wilson Observatory / Carnegie Institution of Washington |volume=675 |pages=1–9 |bibcode=1943CMWCI.675....1B}}</ref> It was the second supernova to be observed in a generation, after [[Tycho Brahe]] observed SN 1572 in [[Cassiopeia A|Cassiopeia]].<ref name="history">{{cite book |last1=Motz |first1=L. |url=https://books.google.com/books?id=sj4qswEACAAJ&q=the+story+of+astronomy+motz |title=The Story of Astronomy |last2=Weaver |first2=J. H. |date=2001 |publisher=[[Basic Books]] |isbn=978-0-7382-0586-1 |page=76 }}</ref>

There is some evidence that the youngest known supernova in our galaxy, [[G1.9+0.3]], occurred in the late 19th century, considerably more recently than [[Cassiopeia A]] from around 1680.<ref name="chakraborti">
{{cite journal |last1=Chakraborti |first1=S. |last2=Childs |first2=F. |last3=Soderberg |first3=A. |author3-link= Alicia M. Soderberg |date=25 February 2016 |title=Young Remnants of type Ia Supernovae and Their Progenitors: A Study Of SNR G1.9+0.3 |journal=The Astrophysical Journal |volume=819 |issue=1 |page=37 |arxiv=1510.08851 |bibcode=2016ApJ...819...37C |doi=10.3847/0004-637X/819/1/37 |s2cid=119246128 |doi-access=free }}</ref> Neither was noted at the time. In the case of G1.9+0.3, high [[Extinction (astronomy)|extinction]] from dust along the plane of the galactic disk could have dimmed the event sufficiently for it to go unnoticed. The situation for Cassiopeia A is less clear; infrared [[light echo]]es have been detected showing that it was not in a region of especially high extinction.<ref name="krause">
{{cite journal |last=Krause |first=O. |date=2008 |title=The Cassiopeia A Supernova was of type IIb |journal=[[Science (journal)|Science]] |volume=320 |issue=5880 |pages=1195–1197 |arxiv=0805.4557 |bibcode=2008Sci...320.1195K |doi=10.1126/science.1155788 |pmid=18511684 |s2cid=40884513}}</ref>
{{multiple image
 |align=right
 |direction=vertical
 |width=200
 |image1=Crab Nebula.jpg
 |alt1=
 |caption1=The [[Crab Nebula]] is a [[pulsar wind nebula]] associated with the [[1054 supernova]].
 |image2=Chinese report of guest star identified as the supernova of 1054 (SN 1054) in the Lidai mingchen zouyi (历代名臣奏议).jpg
 |alt2=
 |caption2=A 1414 text cites a 1055 report: since "the baleful star appeared, a full year has passed and until now its brilliance has not faded".<ref>{{cite journal |bibcode=2006JAHH....9...77P |title=Notes on translations of the East Asian records relating to the supernova of AD 1054 |last1=Pankenier |first1=David W. |journal=Journal of Astronomical History and Heritage |year=2006 |volume=9 |issue=1 |page=77 |doi=10.3724/SP.J.1440-2807.2006.01.06 |s2cid=54914821 }}</ref>
}}

{| class="wikitable float-right"
|+ Historical supernovae in the Local Group
|-
!year
!observed in
! style="width:6em" |maximum apparent brightness
!certainty<ref>{{cite web | title=SNRcat – High Energy Observations of Galactic Supernova Remnants | publisher=University of Manitoba | url=http://snrcat.physics.umanitoba.ca/ | access-date=16 October 2020 }}</ref> of the<br/>SN's identification
|-
| style="text-align:right" |[[SN 185|185]]
|constellation of [[Centaurus]]
| style="text-align:center" |−6'''<sup>[[Apparent magnitude|m]]</sup>'''
|possible SN, but may be a comet<ref>{{cite journal | first1=Y.-N. | last1=Chin | first2=Y.-L. | last2=Huang | journal=Nature | title=Identification of the guest star of AD 185 as a comet rather than a supernova | volume=371 | issue=6496 | pages=398–399 | issn=0028-0836 | date=September 1994 | language=de | doi=10.1038/371398a0 | bibcode=1994Natur.371..398C | s2cid=4240119 | url=http://www.nature.com/articles/371398a0 | access-date=8 November 2021
| url-access=subscription }}</ref><ref>{{cite journal | first1=Fu-Yuan | last1=Zhao | first2=R. G. | last2=Strom | first3=Shi-Yang | last3=Jiang | periodical=Chinese Journal of Astronomy and Astrophysics | title=The Guest Star of AD185 must have been a Supernova | volume=6 | issue=5 | pages=635–640 | issn=1009-9271 | date=October 2006 | language=de | doi=10.1088/1009-9271/6/5/17 | bibcode=2006ChJAA...6..635Z | doi-access=free }}</ref>
|-
| style="text-align:right" |[[SN 386|386]]
|constellation of [[Sagittarius (constellation)|Sagittarius]]
| style="text-align:center" | +1.5'''<sup>m</sup>'''<ref>{{cite book | first=Patrick | last=Moore | title=The Data Book of Astronomy | publisher=CRC Press | year=2000 | pages=295–296 | isbn=978-1-4200-3344-1 | url=https://books.google.com/books?id=fDDpBwAAQBAJ&pg=PA295 }}</ref>
|uncertain whether SN or classical nova<ref name="Hoffmann-2020">{{cite journal | first1=Susanne M. | last1=Hoffmann | first2=Nikolaus | last2=Vogt | journal=Monthly Notices of the Royal Astronomical Society | title=A search for the modern counterparts of the Far Eastern guest stars 369 CE, 386 CE and 393 CE | volume=497 | issue=2 | pages=1419–1433 | bibcode=2020MNRAS.497.1419H | date=1 July 2020 | language=de | doi=10.1093/mnras/staa1970 | doi-access=free | arxiv=2007.01013 }}</ref>
|-
| style="text-align:right" |[[SN 393|393]]
|constellation of [[Scorpius]]
| style="text-align:center" |−3'''<sup>m</sup>'''
|possible SN<ref name="Hoffmann-2020"/>
|-
| style="text-align:right" |[[SN 1006|1006]]
|constellation of [[Lupus (constellation)|Lupus]]
| style="text-align:center" |−7.5{{±|0.4}}'''<sup>m</sup>'''<ref>{{citation | first1=P. Frank | last1=Winkler | first2=G. | last2=Gupta | journal=[[The Astrophysical Journal]] | title=The SN 1006 Reminant: Optical Proper Motions, Deep Imaging, Distance, and Brightness at Maximum | volume=585 | pages=324–335 | date=2003 | issue=1 | language=de | doi=10.1086/345985 | arxiv=astro-ph/0208415 | bibcode=2003ApJ...585..324W | s2cid=1626564 }}</ref>
|certain: [[Supernova remnant|SNR]] known
|-
| style="text-align:right" |[[SN 1054|1054]]
|constellation of [[Taurus (constellation)|Taurus]]
| style="text-align:center" |−6'''<sup>m</sup>'''
|certain: SNR and pulsar known
|-
| style="text-align:right" |[[SN 1181|1181]]
|constellation of [[Cassiopeia (constellation)|Cassiopeia]]
| style="text-align:center" |−2'''<sup>m</sup>'''
|likely Type Iax SN associated with the remnant Pa30<ref>{{citation | first1=Andreas | last1=Ritter | first2=Quentin A. | last2=Parker | first3=Foteini | last3=Lykou | first4=Albert A. | last4=Zijlstra | first5=Martín A. | last5=Guerrero | journal=The Astrophysical Journal Letters | title=The Remnant and Origin of the Historical Supernova 1181 AD | volume=918 | issue=2 | page=L33 | issn=2041-8205 | date=1 September 2021 | language=de | doi=10.3847/2041-8213/ac2253 | arxiv=2105.12384 | bibcode=2021ApJ...918L..33R | hdl=10261/255617 | s2cid=235195784 | doi-access=free }}</ref>
|-
| style="text-align:right" |[[SN 1572|1572]]
|constellation of [[Cassiopeia (constellation)|Cassiopeia]]
| style="text-align:center" |−4'''<sup>m</sup>'''
|certain: SNR known
|-
| style="text-align:right" |[[Kepler's Supernova|1604]]
|constellation of [[Ophiuchus]]
| style="text-align:center" |−2'''<sup>m</sup>'''
|certain: SNR known
|-
| style="text-align:right" |[[Cassiopeia A|1680]]?
|constellation of [[Cassiopeia (constellation)|Cassiopeia]]
| style="text-align:center" | +6'''<sup>m</sup>'''
|SNR known, unclear whether the SN was observed
|-
| style="text-align:right" |[[G1.9+0.3|1800–1900]]
|constellation of [[Sagittarius (constellation)|Sagittarius]]
| style="text-align:center" | ?'''<sup>m</sup>'''
|SNR known, but not observed
|-
| style="text-align:right" |[[SN 1885A|1885]]
|[[The Andromeda Galaxy|Andromeda Galaxy]]
| style="text-align:center" | +6'''<sup>m</sup>'''
|certain
|-
| style="text-align:right" |[[SN 1987A|1987]]
|[[Large Magellanic Cloud]]
| style="text-align:center" | +3'''<sup>m</sup>'''
|certain
|}

===Telescope findings===
With the development of the astronomical [[telescope]], observation and discovery of fainter and more distant supernovae became possible. The first such observation was of [[SN 1885A]] in the [[Andromeda Galaxy]]. A second supernova, [[SN 1895B]], was discovered in [[NGC 5253]] a decade later.<ref name=Schaefer1995>{{cite journal
 | title=The Peak Brightness of SN 1895B in NGC 5253 and the Hubble Constant
 | last=Schaefer | first=Bradley E.
 | journal=Astrophysical Journal Letters
 | volume=447 | page=L13 | date=July 1995
 | doi=10.1086/309549 | bibcode=1995ApJ...447L..13S | s2cid=227285055 | doi-access=free }}</ref> Early work on what was originally believed to be simply a new category of [[nova]]e was performed during the 1920s. These were variously called "upper-class Novae", "Hauptnovae", or "giant novae".<ref>{{cite book
 | title=Classifying the Cosmos: How We Can Make Sense of the Celestial Landscape
 | first=Steven J. | last=Dick | year=2019
 | page=191 | isbn=978-3-030-10380-4
 | publisher=Springer International Publishing
 | url=https://books.google.com/books?id=UymODwAAQBAJ&pg=PA191
}}</ref> The name "supernovae" is thought to have been coined by [[Walter Baade]] and Zwicky in lectures at [[Caltech]] in 1931. It was used, as "super-Novae", in a journal paper published by [[Knut Lundmark]] in 1933,<ref name="baas33_1330">{{cite journal
 |last1=Osterbrock |first1=D. E.
 |year=2001
 |title=Who Coined the Word Supernova? Who First Predicted Neutron Stars?
 |journal=[[Bulletin of the American Astronomical Society]]
 |volume=33 |page=1330
 |bibcode=2001AAS...199.1501O
}}</ref> and in a 1934 paper by Baade and Zwicky.<ref name="Baade1934">
{{cite journal |last1=Baade |first1=Walter |last2=Zwicky |first2=Fritz |date=1934 |title=On Super-novae |journal=[[Proceedings of the National Academy of Sciences]] |volume=20 |issue=5 |pages=254–259 |bibcode=1934PNAS...20..254B |doi=10.1073/pnas.20.5.254 |pmc=1076395 |pmid=16587881 |doi-access=free}}</ref> By 1938, the hyphen was no longer used and the modern name was in use.<ref>
{{cite book
 |last1=Murdin
 |first1=P.
 |last2=Murdin
 |first2=L.
 |year=1985
 |title=Supernovae
 |page=[https://archive.org/details/supernovae00murd/page/42 42]
 |edition=2nd
 |publisher=[[Cambridge University Press]]
 |isbn=978-0-521-30038-4
 |url=https://archive.org/details/supernovae00murd/page/42
 }}</ref>

American astronomers [[Rudolph Minkowski]] and [[Fritz Zwicky]] developed the modern supernova classification scheme beginning in 1941.<ref>
{{Cite journal
 |last=da Silva |first=L. A. L.
 |date=1993
 |title=The Classification of Supernovae
 |journal=[[Astrophysics and Space Science]]
 |volume=202 |issue=2 |pages=215–236
 |bibcode=1993Ap&SS.202..215D
 |doi=10.1007/BF00626878
|s2cid=122727067
 }}</ref> During the 1960s, astronomers found that the maximum intensities of supernovae could be used as [[standard candles]], hence indicators of astronomical distances.<ref>
{{Cite journal
 |last=Kowal |first=C. T.
 |date=1968
 |title=Absolute magnitudes of supernovae
 |journal=[[Astronomical Journal]]
 |volume=73 |pages=1021–1024
 |bibcode=1968AJ.....73.1021K
 |doi=10.1086/110763
|doi-access=free
 }}</ref> Some of the most distant supernovae observed in 2003 appeared dimmer than expected. This supports the view that the expansion of the [[Accelerating universe|universe is accelerating]].<ref name="Leibundgut">
{{cite journal
 |last1=Leibundgut |first1=B.
 |year=2003
 |title=A cosmological surprise: The universe accelerates
 |journal=Europhysics News
 |volume=32 |issue=4 |pages=121–125
 |bibcode=2001ENews..32..121L
 |doi=10.1051/epn:2001401
|doi-access=free
 }}</ref> Techniques were developed for reconstructing supernovae events that have no written records of being observed. The date of the Cassiopeia A supernova event was determined from light echoes off [[nebula]]e,<ref>
{{Cite journal
 |last=Fabian |first=A. C.
 |date=2008
 |title=A Blast from the Past
 |journal=[[Science (journal)|Science]]
 |volume=320 |issue=5880 |pages=1167–1168
 |doi=10.1126/science.1158538
 |pmid=18511676
|s2cid=206513073
 }}</ref> while the age of supernova remnant [[RX J0852.0-4622]] was estimated from temperature measurements<ref>
{{Cite journal
 |last=Aschenbach |first=B.
 |date=1998
 |title=Discovery of a young nearby supernova remnant
 |journal=[[Nature (journal)|Nature]]
 |volume=396 |issue=6707 |pages=141–142
 |bibcode=1998Natur.396..141A
 |doi=10.1038/24103
|s2cid=4426317
 }}</ref> and the [[gamma ray]] emissions from the radioactive decay of [[titanium-44]].<ref>
{{Cite journal
 |last1=Iyudin |first1=A. F.
 |last2=Schönfelder |first2=V.
 |last3=Bennett |first3=K.
 |last4=Bloemen |first4=H.
 |last5=Diehl |first5=R.
 |last6=Hermsen |first6=W.
 |last7=Lichti |first7=G. G.
 |last8=Van Der Meulen |first8=R. D.
 |last9=Ryan |first9=J.
 |last10=Winkler |first10=C.
 |date=1998
 |title=Emission from <sup>44</sup>Ti associated with a previously unknown Galactic supernova
 |journal=[[Nature (journal)|Nature]]
 |volume=396 |issue=6707 |pages=142–144
 |bibcode=1998Natur.396..142I
 |doi=10.1038/24106
|s2cid=4430526
 }}</ref>

[[File:Jades Deep Field Annotated.png|thumb|upright=1.2|Jades Deep Field. A team of astronomers studying JADES data identified about 80 objects (circled in green) that changed in brightness over time. Most of these objects, known as transients, are the result of exploding stars or supernovae.<ref>{{cite web |title=NASA's Webb Opens New Window on Supernova Science - NASA Science |url=https://science.nasa.gov/missions/webb/nasas-webb-opens-new-window-on-supernova-science |website=science.nasa.gov |date=10 June 2024 |access-date=11 June 2024}}</ref>]]

The most luminous supernova ever recorded is [[ASASSN-15lh]], at a distance of 3.82 [[light-year|gigalight-years]]. It was first detected in June 2015 and peaked at {{solar luminosity|570 billion|link=y}}, which is twice the [[bolometric luminosity]] of any other known supernova.<ref>{{Cite journal
 | last1=Dong | first1=Subo | last2=Shappee | first2=B. J.
 | last3=Prieto | first3=J. L. | last4=Jha | first4=S. W.
 | last5=Stanek | first5=K. Z. | last6=Holoien | first6=T. W. -S.
 | last7=Kochanek | first7=C. S. | last8=Thompson | first8=T. A.
 | last9=Morrell | first9=N. | last10=Thompson | first10=I. B.
 | last11=Basu | first11=U. | last12=Beacom | first12=J. F.
 | last13=Bersier | first13=D. | last14=Brimacombe | first14=J.
 | last15=Brown | first15=J. S. | last16=Bufano | first16=F.
 | last17=Chen | first17=Ping | last18=Conseil | first18=E.
 | last19=Danilet | first19=A. B. | last20=Falco | first20=E.
 | last21=Grupe | first21=D. | last22=Kiyota | first22=S.
 | last23=Masi | first23=G. | last24=Nicholls | first24=B.
 | last25=Olivares E. | first25=F. | last26=Pignata | first26=G.
 | last27=Pojmanski | first27=G. | last28=Simonian | first28=G. V.
 | last29=Szczygiel | first29=D. M. | last30=Woźniak | first30=P. R.
 | title=ASASSN-15lh: A highly super-luminous supernova
 | journal=Science | year=2016 | s2cid=31444274
 | volume=351 | issue=6270 | pages=257–260
 | arxiv=1507.03010 | bibcode=2016Sci...351..257D
 | doi=10.1126/science.aac9613 | pmid=26816375
}}</ref> The nature of this supernova is debated and several alternative explanations, such as tidal disruption of a star by a black hole, have been suggested.<ref>
{{Cite journal
 | title=The superluminous transient ASASSN-15lh as a tidal disruption event from a Kerr black hole
 | last1=Leloudas | first1=G. | last2=Fraser | first2=M.
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[[SN 2013fs]] was recorded three hours after the supernova event on 6 October 2013, by the [[Palomar Transient Factory|Intermediate Palomar Transient Factory]]. This is among the earliest supernovae caught after detonation, and it is the earliest for which spectra have been obtained, beginning six hours after the actual explosion. The star is located in a [[spiral galaxy]] named [[NGC 7610]], 160&nbsp;million light-years away in the constellation of Pegasus.<ref>
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The supernova [[SN 2016gkg]] was detected by amateur astronomer Victor Buso from [[Rosario]], Argentina, on 20 September 2016.<ref name=AS_Now>{{cite magazine
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|title=Amateur astronomer makes once-in-lifetime discovery
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{{cite journal
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 |last18=Nomoto |first18=K.
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 |date=21 February 2018
|title=A surge of light at the birth of a supernova
 |journal=[[Nature (journal)|Nature]]
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 |arxiv=1802.09360
 |bibcode=2018Natur.554..497B
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|s2cid=4383303
 }}</ref> It was the first time that the initial "shock breakout" from an optical supernova had been observed.<ref name=AS_Now/> The progenitor star has been identified in [[Hubble Space Telescope]] images from before its collapse. Astronomer [[Alex Filippenko]] noted: "Observations of stars in the first moments they begin exploding provide information that cannot be directly obtained in any other way."<ref name=AS_Now/>

===Discovery programs===
[[File:NASA-SNR0519690-ChandraXRayObservatory-20150122.jpg|thumb|[[Supernova remnant]] SNR E0519-69.0 in the [[Large Magellanic Cloud]]]]

Because supernovae are relatively rare events within a galaxy, occurring about three times a century in the Milky Way,<ref name="reynolds">
{{cite journal
 |last1=Reynolds |first1=S. P.
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 |last6=Petre |first6=R.
 |year=2008
 |title=The Youngest Galactic Supernova Remnant: G1.9+0.3
 |journal=[[The Astrophysical Journal Letters]]
 |volume=680 |issue=1 |pages=L41–L44
 |arxiv=0803.1487
 |bibcode=2008ApJ...680L..41R
 |doi=10.1086/589570
|s2cid=67766657
 }}</ref> obtaining a good sample of supernovae to study requires regular monitoring of many galaxies. Today, amateur and professional astronomers are finding about two thousand every year, some when near maximum brightness, others on old astronomical photographs or plates. Supernovae in other galaxies cannot be predicted with any meaningful accuracy. Normally, when they are discovered, they are already in progress.<ref>
{{cite journal
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 |journal=[[The Astrophysical Journal]]
 |volume=157 |page=623
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 |doi=10.1086/150102
}}</ref> To use supernovae as [[standard candle]]s for measuring distance, observation of their peak luminosity is required. It is therefore important to discover them well before they reach their maximum. [[Amateur astronomy|Amateur astronomers]], who greatly outnumber professional astronomers, have played an important role in finding supernovae, typically by looking at some of the closer galaxies through an [[optical telescope]] and comparing them to earlier photographs.<ref>
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Toward the end of the 20th century, astronomers increasingly turned to computer-controlled telescopes and [[charge-coupled device|CCDs]] for hunting supernovae. While such systems are popular with amateurs, there are also professional installations such as the [[Katzman Automatic Imaging Telescope]].<ref>
{{cite conference
 |last1=Filippenko |first1=A. V.
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 |editor1-last=Paczynski |editor1-first=B.
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}}</ref> The [[Supernova Early Warning System]] (SNEWS) project uses a network of [[neutrino detector]]s to give early warning of a supernova in the Milky Way galaxy.<ref name="Antonioli-2004">
{{Cite journal
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 |date=2004
 |title=SNEWS: The SuperNova Early Warning System
 |journal=[[New Journal of Physics]]
 |volume=6 |page=114
 |arxiv=astro-ph/0406214
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{{cite journal
 |last1=Scholberg |first1=K.|author-link= Kate Scholberg
 |year=2000
 |title=SNEWS: The supernova early warning system
 |journal=[[AIP Conference Proceedings]]
 |volume=523 |pages=355–361
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 |bibcode=2000AIPC..523..355S
 |citeseerx=10.1.1.314.8663
 |doi=10.1063/1.1291879
|s2cid=5803494}}</ref> [[Neutrino]]s are [[subatomic particle]]s that are produced in great quantities by a supernova, and they are not significantly absorbed by the interstellar gas and dust of the galactic disk.<ref>
{{cite journal
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[[File:A star set to explode.jpg|thumbnail|left|upright=1.2|"A star set to explode", the SBW1 nebula surrounds a massive blue supergiant in the [[Carina Nebula]].]]

Supernova searches fall into two classes: those focused on relatively nearby events and those looking farther away. Because of the [[expansion of the universe]], the distance to a remote object with a known [[emission spectrum]] can be estimated by measuring its [[Doppler shift]] (or [[redshift]]); on average, more-distant objects recede with greater velocity than those nearby, and so have a higher redshift. Thus the search is split between high redshift and low redshift, with the boundary falling around a redshift range of z=0.1–0.3, where z is a dimensionless measure of the spectrum's frequency shift.<ref>
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High redshift searches for supernovae usually involve the observation of supernova light curves. These are useful for standard or calibrated candles to generate [[Hubble diagram]]s and make cosmological predictions. Supernova spectroscopy, used to study the physics and environments of supernovae, is more practical at low than at high redshift.<ref>
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As survey programmes rapidly increase the number of detected supernovae, collated collections of observations (light decay curves, astrometry, pre-supernova observations, spectroscopy) have been assembled. The Pantheon data set, assembled in 2018, detailed 1048 supernovae.<ref> {{Cite journal
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 }}</ref> In 2021, this data set was expanded to 1701 light curves for 1550 supernovae taken from 18 different surveys, a 50% increase in under 3 years.<ref> {{Cite journal
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 }}</ref>

==Naming convention==
[[Image:Keplers supernova.jpg|thumb|Multi-wavelength [[X-ray]], [[infrared]], and [[optical]] compilation image of [[Johannes Kepler|Kepler's]] [[supernova remnant]], [[SN 1604]]]]Supernova discoveries are reported to the [[International Astronomical Union]]'s [[Central Bureau for Astronomical Telegrams]], which sends out a circular with the name it assigns to that supernova.<ref>{{Cite web |title=What Kinds of Discovered Objects to Report for IAUC Publication |url=http://www.cbat.eps.harvard.edu/WhatToReport.html |access-date=2023-03-08 |website=cbat.eps.harvard.edu}}</ref> The name is formed from the prefix ''SN'', followed by the year of discovery, suffixed with a one or two-letter designation. The first 26 supernovae of the year are designated with a capital letter from ''A'' to ''Z''. Next, pairs of lower-case letters are used: ''aa'', ''ab'', and so on. Hence, for example, ''SN 2003C'' designates the third supernova reported in the year 2003.<ref>{{cite journal
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 |journal=[[AIP Conference Proceedings]]
 |volume=63
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 |hdl=2027.42/87614
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 |url-status=live
 }}</ref> The last supernova of 2005, SN 2005nc, was the 367th (14 × 26 + 3 = 367). Since 2000, professional and amateur astronomers have been finding several hundred supernovae each year (572 in 2007, 261 in 2008, 390 in 2009; 231 in 2013).<ref>
{{cite web
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{{cite web
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 |archive-date=10 January 2014
}}</ref>

Historical supernovae are known simply by the year they occurred: SN 185, SN 1006, SN 1054, SN 1572 (called ''Tycho's Nova'') and SN 1604 (''Kepler's Star'').<ref>{{Cite book |last1=Stephenson |first1=F. Richard |title=Historical Supernovae and Their Remnants |date=2002 |publisher=Clarendon Press |first2=David A. |last2=Green |isbn=0-19-850766-6 |location=Oxford |oclc=50403827 |pages=1&ndash;5, 60, 82}}</ref> Since 1885 the additional letter notation has been used, even if there was only one supernova discovered that year (for example, SN 1885A, SN 1907A, etc.); this last happened with SN 1947A. ''SN'', for SuperNova, is a standard prefix. Until 1987, two-letter designations were rarely needed; since 1988, they have been needed every year. Since 2016, the increasing number of discoveries has regularly led to the additional use of three-letter designations.<ref>{{cite web| url = https://sne.space/| title = Open Supernova Catalog| access-date = 5 February 2020| archive-date = 3 March 2016| archive-url = https://web.archive.org/web/20160303230459/https://sne.space/| url-status = live}}</ref> After zz comes aaa, then aab, aac, and so on. For example, the last supernova retained in the Asiago Supernova Catalogue&thinsp; when it was terminated on 31 December 2017 bears the designation SN 2017jzp.<!-- SN 2017jmk was the last addition to the catalogue, but jzp is the highest-lettered designation --><ref>Padova-Asiago Supernova Group, [http://graspa.oapd.inaf.it/asnc.html Asiago Supernova Catalogue], accessed 2023-12-27</ref>

==Classification==
Astronomers classify supernovae according to their [[light curve]]s and the [[absorption line]]s of different [[chemical element]]s that appear in their [[Astronomical spectroscopy|spectra]]. If a supernova's spectrum contains lines of [[hydrogen]] (known as the [[Balmer series]] in the visual portion of the spectrum) it is classified ''Type II''; otherwise it is ''Type I''. In each of these two types there are subdivisions according to the presence of lines from other elements or the shape of the light curve (a graph of the supernova's apparent magnitude as a function of time).<ref name="types">
{{cite conference
 |last1=Cappellaro |first1=E.
 |last2=Turatto |first2=M.
 |title=The Influence of Binaries on Stellar Population Studies
 |date=2001
 |chapter=Supernova Types and Rates
 |series=Astrophysics and Space Science Library
 |book-title=Influence of Binaries on Stellar Population Studies
 |volume=264 |page=199
 |publisher=[[Kluwer Academic Publishers]]
 |location=Dordrecht
 |arxiv=astro-ph/0012455
 |bibcode=2001ASSL..264..199C
 |doi=10.1007/978-94-015-9723-4_16
 |isbn=978-0-7923-7104-5
}}</ref><ref name="taxonomy"/>

{|class="wikitable"
|+Supernova taxonomy<ref name="types"/><ref name="taxonomy"/>
|rowspan="3" style="background:#ccc; valign:center;"|Type I<br/>No hydrogen
|colspan="4"|[[Type Ia supernova|Type Ia]]<br/>Presents a singly [[ionization|ionised]] [[silicon]] (Si II) line at 615.0 [[Nanometre|nm]] (nanometers), near peak light
|colspan="4" style="background:#fff;"|[[#Thermal runaway|Thermal runaway]]
|-
|rowspan="2" style="background:#eee; valign:center;"|[[Type Ib and Ic supernovae|Type Ib/c]]<br/>Weak or no silicon absorption feature
|colspan="3"|Type Ib<br/>Shows a non-ionised [[helium]] (He I) line at 587.6&nbsp;nm
|rowspan="6" style="background:#fff;"|[[#Core collapse|Core collapse]]
|-
|colspan="3"|Type Ic<br/>Weak or no helium
|-
|rowspan="4" style="background:#ccc; valign:center;"|[[Type II supernova|Type II]]<br/>Shows hydrogen
|rowspan="3" style="background:#ddd; valign:center;"|[[Type II supernova|Type II-P/-L/n]]<br/>Type II spectrum throughout
|rowspan="2" colspan="2" style="background:#eee; valign:center;"|[[Type II supernova#Light curves for Type II-L and Type II-P supernovae|Type II-P/L]]<br/>No narrow lines
|[[Type II supernova#Light curves for Type II-L and Type II-P supernovae|Type II-P]]<br/>Reaches a "plateau" in its light curve
|-
|[[Type II supernova#Light curves for Type II-L and Type II-P supernovae|Type II-L]]<br/>Displays a "linear" decrease in its light curve (linear in magnitude versus time)<ref name="doggett"/>
|-
|colspan="3"|[[Type II supernova#Type IIn supernovae|Type IIn]]<br/>Some narrow lines
|-
|colspan="4"|[[Type II supernova#Type IIb supernovae|Type IIb]]<br/>Spectrum changes to become like Type Ib
|}

===Type I===
[[File:SN2018gv.gif|thumb|upright=1.5|Light curve for Type Ia [[NGC 2525#SN 2018gv|SN 2018gv]]]]

Type I supernovae are subdivided on the basis of their spectra, with Type Ia showing a strong [[Silicon|ionised silicon]] absorption line. Type I supernovae without this strong line are classified as Type Ib and Ic, with Type Ib showing strong neutral helium lines and Type Ic lacking them. Historically, the light curves of Type I supernovae were seen as all broadly similar, too much so to make useful distinctions.<ref name="doggett"/> While variations in light curves have been studied, classification continues to be made on spectral grounds rather than light-curve shape.<ref name="taxonomy"/>

A small number of Type Ia supernovae exhibit unusual features, such as non-standard luminosity or broadened light curves, and these are typically categorised by referring to the earliest example showing similar features. For example, the sub-luminous [[SN 2008ha]] is often referred to as [[SN 2002cx]]-like or class Ia-2002cx.<ref name=foley2008>{{cite journal|doi=10.1088/0004-6256/138/2/376|arxiv=0902.2794|title=SN 2008ha: an extremely low luminosity and exceptionally low energy supernova|date=2009|last1=Foley|first1=Ryan J.|journal=The Astronomical Journal|volume=138|page=376|last2=Chornock|first2=Ryan|last3=Filippenko|first3=Alexei V.|last4=Ganeshalingam|first4=Mohan|last5=Kirshner|first5=Robert P.|last6=Li|first6=Weidong|last7=Cenko|first7=S. Bradley|last8=Challis|first8=Peter J.|last9=Friedman|first9=Andrew S.|last10=Modjaz|first10=Maryam|last11=Silverman|first11=Jeffrey M.|last12=Wood-Vasey|first12=W. Michael|bibcode=2009AJ....138..376F|issue=2|s2cid=13855329}}</ref>

A small proportion of Type Ic supernovae show highly broadened and blended emission lines which are taken to indicate very high expansion velocities for the ejecta. These have been classified as Type Ic-BL or Ic-bl.<ref name=bianco>
{{cite journal
 |last1=Bianco |first1=F. B.
 |last2=Modjaz |first2=M.
 |last3=Hicken |first3=M.
 |last4=Friedman |first4=A.
 |last5=Kirshner |first5=R. P.
 |last6=Bloom |first6=J. S.
 |last7=Challis |first7=P.
 |last8=Marion |first8=G. H.
 |last9=Wood-Vasey |first9=W. M.
 |last10=Rest |first10=A.
 |year=2014
 |title=Multi-color Optical and Near-infrared Light Curves of 64 Stripped-envelope Core-Collapse Supernovae
 |journal=The Astrophysical Journal Supplement
 |volume=213|issue=2|page=19
 |arxiv=1405.1428
 |bibcode=2014ApJS..213...19B
 |doi=10.1088/0067-0049/213/2/19
|s2cid=119243970
 }}</ref>

[[Calcium-rich supernova]]e are a rare type of very fast supernova with unusually strong calcium lines in their spectra.<ref>{{Cite journal |last1=Lyman |first1=J. D. |last2=Levan |first2=A. J. |last3=James |first3=P. A. |last4=Angus |first4=C. R. |last5=Church |first5=R. P. |last6=Davies |first6=M. B. |last7=Tanvir |first7=N. R. |date=2016-05-11 |title=Hubble Space Telescope observations of the host galaxies and environments of calcium-rich supernovae |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=458 |issue=2 |pages=1768–1777 |doi=10.1093/mnras/stw477 |issn=0035-8711|doi-access=free |arxiv=1602.08098 }}</ref><ref>{{Cite journal |last=Nugent |first=Peter |date=2017-06-02 |title=Supernovae: The explosion in a bubble |url=https://www.nature.com/articles/s41550-017-0140 |journal=Nature Astronomy |language=en |volume=1 |issue=6 |article-number=0140 |doi=10.1038/s41550-017-0140 |bibcode=2017NatAs...1E.140N |osti=1456969 |s2cid=125998037 |issn=2397-3366}}</ref> Models suggest they occur when material is accreted from a [[helium]]-rich companion rather than a [[hydrogen]]-rich star. Because of helium lines in their spectra, they can resemble Type Ib supernovae, but are thought to have very different progenitors.<ref name="Perets-2010">{{cite journal |doi=10.1038/nature09056 |title=A faint type of supernova from a white dwarf with a helium-rich companion |year=2010 |last1=Perets |first1=H. B. |last2=Gal-Yam |first2=A. |last3=Mazzali |first3=P. A. |last4=Arnett |first4=D. |last5=Kagan |first5=D. |last6=Filippenko |first6=A. V. |last7=Li |first7=W. |last8=Arcavi |first8=I. |last9=Cenko |first9=S. B. |last10=Fox |first10=D. B. |last11=Leonard |first11=D. C. |last12=Moon |first12=D.-S. |last13=Sand |first13=D. J. |last14=Soderberg |first14=A. M. |last15=Anderson |first15=J. P. |last16=James |first16=P. A. |last17=Foley |first17=R. J. |last18=Ganeshalingam |first18=M. |last19=Ofek |first19=E. O. |last20=Bildsten |first20=L. |last21=Nelemans |first21=G. |last22=Shen |first22=K. J. |last23=Weinberg |first23=N. N. |last24=Metzger |first24=B. D. |last25=Piro |first25=A. L. |last26=Quataert |first26=E. |last27=Kiewe |first27=M. |last28=Poznanski |first28=D. |journal=Nature |volume=465 |issue=7296 |pages=322–325 |pmid=20485429 |arxiv=0906.2003 |bibcode=2010Natur.465..322P |s2cid=4368207 }}</ref>

Type Ien has been proposed to explain observations of the supernova [[SN 2021yfj]].<ref name="schulze">{{Cite journal  | last1=Schulze
 | first1=Steve  | last2=Gal-Yam  | first2=Avishay  | last3=Dessart  | first3=Luc  | last4=Miller  | first4=Adam A.  | last5=Woosley  | first5=Stan E.
 | title=Extremely stripped supernova reveals a silicon and sulfur formation site  | journal=Nature  | date=20 August 2025  | volume=644  | issue=8077
 | pages=634–639  | doi=10.1038/s41586-025-09375-3  | pmid=40836132 | arxiv=2409.02054 | bibcode=2025Natur.644..634S }}</ref> Having lost its outer layers of hydrogen, helium and carbon, the star, just before the explosion, released an unusual, hidden layer of [[silicon]], [[sulfur]] and [[argon]], elements that are not often seen in dying stars.<ref name="cnn">{{cite news  | last       = Strickland  | first      = Ashley  | title      = Astronomers discover rare new type of supernova  | url        = https://edition.cnn.com/2025/08/22/science/new-supernova-discovery  | work       = CNN  | date       = 22 August 2025  | access-date= 23 August 2025 }}</ref> During the explosion, the material from the star's [[Stellar core|core]] collided with the gaseous shell, and the heat of the collision caused the silicon and sulfur layer to glow. The explosion showed that stars can be completely stripped down and still produce a brilliant explosion observable from very far distance. The discovery provided direct evidence of the long-theorized, but difficult to observe, [[Stellar structure|internal structure]] of [[Star#Massive stars|massive stars]].<ref name="cnn"/> In the type's name, "e" describes the position of the silicon/sulfur layer in the internal structure, while "n" signifies narrow emission lines.<ref name="schulze"/>

===Type II===
[[Image:SNIIcurva.svg|thumb|Light curves are used to classify Type II-P and Type II-L supernovae.<ref name="taxonomy"/><ref name="barbon1979"/>]]
The supernovae of [[Type II supernova|Type II]] can also be sub-divided based on their spectra. While most Type II supernovae show very broad [[emission line]]s which indicate expansion velocities of many thousands of [[kilometres per second]], some, such as [[SN 2005gl]], have relatively narrow features in their spectra. These are called Type IIn, where the "n" stands for "narrow".<ref name="taxonomy"/>

A few supernovae, such as SN 1987K<ref>{{cite journal |last1=Filippenko |first1=A. V. |title=Supernova 1987K: Type II in Youth, Type Ib in Old Age |journal=The Astronomical Journal |date=1988 |volume=96 |page=1941 |doi=10.1086/114940 |bibcode=1988AJ.....96.1941F}}</ref> and [[SN 1993J]], appear to change types: they show lines of hydrogen at early times, but, over a period of weeks to months, become dominated by lines of helium. The term [[Type IIb supernova|"Type IIb"]] is used to describe the combination of features normally associated with Type II and Type Ib.<ref name="taxonomy"/>

Type II supernovae with normal spectra dominated by broad hydrogen lines that remain for the life of the decline are classified on the basis of their light curves. The most common type shows a distinctive "plateau" in the light curve shortly after peak brightness where the visual luminosity stays relatively constant for several months before the decline resumes. These are called Type II-P referring to the plateau. Less common are Type II-L supernovae that lack a distinct plateau. The "L" signifies "linear" although the light curve is not actually a straight line.<ref name="taxonomy"/>

Supernovae that do not fit into the normal classifications are designated peculiar, or "pec".<ref name="taxonomy">
{{cite book
 |last1=Turatto |first1=M.
 |year=2003
 |chapter=Classification of Supernovae
 |title=Supernovae and Gamma-Ray Bursters
 |volume=598 |pages=21–36
 |series=[[Lecture Notes in Physics]]
 |arxiv=astro-ph/0301107
 |citeseerx=10.1.1.256.2965
 |doi=10.1007/3-540-45863-8_3
 |isbn=978-3-540-44053-6
|s2cid=15171296
 }}</ref>

===Types III, IV and V===
Zwicky defined additional supernovae types based on a very few examples that did not cleanly fit the parameters for Type I or Type II supernovae. [[SN 1961i]] in [[NGC 4303]] was the prototype and only member of the Type III supernova class, noted for its broad light curve maximum and broad hydrogen Balmer lines that were slow to develop in the spectrum.<ref name="doggett"/> SN 1961f in [[NGC 3003]] was the prototype and only member of the Type IV class, with a light curve similar to a Type II-P supernova, with [[hydrogen absorption line]]s but weak [[hydrogen emission line]]s.<ref name="doggett"/> The Type V class was coined for [[SN 1961V]] in [[NGC 1058]], an unusual faint supernova or [[supernova impostor]] with a slow rise to brightness, a maximum lasting many months, and an unusual emission spectrum. The similarity of SN 1961V to the [[Eta Carinae]] Great Outburst was noted.<ref name="zwicky2">
{{cite journal
 |last1=Zwicky |first1=F.
 |year=1964
 |title=NGC 1058 and its Supernova 1961
 |journal=[[The Astrophysical Journal]]
 |volume=139 |page=514
 |bibcode=1964ApJ...139..514Z
 |doi=10.1086/147779
|doi-access=free
 }}</ref> Supernovae in M101 (1909) and M83 (1923 and 1957) were also suggested as possible Type IV or Type V supernovae.<ref name="zwicky">
{{cite conference
 |last=Zwicky |first=F.
 |year=1962
 |title=New Observations of Importance to Cosmology
 |editor-last=McVittie |editor-first=G. C.
 |book-title=Problems of Extra-Galactic Research, Proceedings from IAU Symposium
 |volume=15 |page=347
 |publisher=[[Macmillan Press]]
 |location=New York
 |bibcode=1962IAUS...15..347Z
}}</ref>

These types would now all be treated as peculiar Type II supernovae (IIpec), of which many more examples have been discovered, although it is still debated whether SN 1961V was a true supernova following an [[Luminous blue variable|LBV]] outburst or an impostor.<ref name="doggett">
{{cite journal
 |last1=Doggett |first1=J. B.
 |last2=Branch |first2=D.
 |year=1985
 |title=A comparative study of supernova light curves
 |journal=[[The Astronomical Journal]]
 |volume=90 |page=2303
 |bibcode=1985AJ.....90.2303D
 |doi=10.1086/113934
|doi-access=free
 }}</ref><ref>{{Cite journal |last=Filippenko |first=Alexei V. |date=September 1997 |title=Optical Spectra of Supernovae |url=https://www.annualreviews.org/doi/10.1146/annurev.astro.35.1.309 |journal=Annual Review of Astronomy and Astrophysics |language=en |volume=35 |issue=1 |pages=309–355 |doi=10.1146/annurev.astro.35.1.309 |bibcode=1997ARA&A..35..309F |issn=0066-4146 |quote=SN 1961V in NGC 1058 (Type V) had the most bizarre light curve ever recorded.|url-access=subscription }}</ref>

==Current models==
[[File:The Rise and Fall of a Supernova.jpg|thumb|upright=1.7|In the galaxy [[NGC 1365]] a supernova (the bright dot slightly above the galactic center) rapidly brightens, then fades more slowly.<ref>
{{cite news
 |title=The Rise and Fall of a Supernova
 |url=http://www.eso.org/public/images/potw1323a/
 |newspaper=ESO Picture of the Week
 |access-date=14 June 2013
|url-status=live
 |archive-url=https://web.archive.org/web/20130702042133/http://www.eso.org/public/images/potw1323a/
 |archive-date=2 July 2013
}}</ref>]]

Supernova type codes, as summarised in the table above, are ''[[Taxonomy (general)|taxonomic]]'': the type number is based on the light observed from the supernova, not necessarily its cause. For example, Type Ia supernovae are produced by runaway fusion ignited on degenerate white dwarf progenitors, while the spectrally similar Type Ib/c are produced from massive stripped progenitor stars by core collapse.

===Thermal runaway===
{{Main|Type Ia supernova}}
[[File:Progenitor IA supernova.svg|thumb|upright=1.7|Formation of a Type Ia supernova]]
A white dwarf star may accumulate sufficient material from a stellar companion to raise its core temperature enough to [[Carbon detonation|ignite]] [[Carbon burning process|carbon fusion]], at which point it undergoes [[Thermal runaway|runaway]] nuclear fusion, completely disrupting it. There are three avenues by which this detonation is theorised to happen: stable [[accretion (astrophysics)|accretion]] of material from a companion, the collision of two white dwarfs, or accretion that causes ignition in a shell that then ignites the core. The dominant mechanism by which Type Ia supernovae are produced remains unclear.<ref name="Piro2014">
{{Cite journal
 |last1=Piro |first1=A. L.
 |last2=Thompson |first2=T. A.
 |last3=Kochanek |first3=C. S.
 |year=2014
 |title=Reconciling 56Ni production in Type Ia supernovae with double degenerate scenarios
 |journal=[[Monthly Notices of the Royal Astronomical Society]]
 |volume=438 |issue=4 |page=3456
 |arxiv=1308.0334
 |bibcode=2014MNRAS.438.3456P
 |doi=10.1093/mnras/stt2451
|doi-access=free
 |s2cid=27316605
 }}</ref> Despite this uncertainty in how Type Ia supernovae are produced, Type Ia supernovae have very uniform properties and are useful [[Cosmic distance ladder|standard candles]] over intergalactic distances. Some calibrations are required to compensate for the gradual change in properties or different frequencies of abnormal luminosity supernovae at high redshift, and for small variations in brightness identified by light curve shape or spectrum.<ref name="chen">
{{Cite journal
 |last1=Chen |first1=W.-C.
 |last2=Li |first2=X.-D.
 |year=2009
 |title=On the Progenitors of Super-Chandrasekhar Mass Type Ia Supernovae
 |journal=[[The Astrophysical Journal]]
 |volume=702 |issue=1|pages=686–691
 |arxiv=0907.0057
 |bibcode=2009ApJ...702..686C
 |doi=10.1088/0004-637X/702/1/686
|s2cid=14301164
 }}</ref><ref>
{{Cite journal
 |last1=Howell |first1=D. A.
 |last2=Sullivan |first2=M.
 |last3=Conley |first3=A. J.
 |last4=Carlberg |first4=R. G.
 |date=2007
 |title=Predicted and Observed Evolution in the Mean Properties of Type Ia Supernovae with Redshift
 |journal=[[Astrophysical Journal Letters]]
 |volume=667 |issue=1 |pages=L37–L40
 |arxiv=astro-ph/0701912
 |bibcode=2007ApJ...667L..37H
 |doi=10.1086/522030
|s2cid=16667595
 }}</ref>

====Normal Type Ia====
There are several means by which a supernova of this type can form, but they share a common underlying mechanism. If a [[carbon]]-[[oxygen]] white dwarf accreted enough matter to reach the [[Chandrasekhar limit]] of about 1.44 [[solar mass]]es<ref name="Mazzali2007">
{{Cite journal
 |last1=Mazzali |first1=P. A.
 |last2=Röpke |first2=F. K.
 |last3=Benetti |first3=S.
 |last4=Hillebrandt |first4=W.
 |date=2007
 |title=A Common Explosion Mechanism for Type Ia Supernovae
 |journal=[[Science (journal)|Science]]
 |volume=315 |issue=5813 |pages=825–828
 |arxiv=astro-ph/0702351
 |bibcode=2007Sci...315..825M
 |doi=10.1126/science.1136259
 |pmid=17289993
|s2cid=16408991
 }}</ref> (for a non-rotating star), it would no longer be able to support the bulk of its mass through [[electron degeneracy pressure]]<ref name="Chandrasekhar">{{Cite journal
 |last1=Lieb
 |first1=E. H.
 |last2=Yau
 |first2=H.-T.
 |date=1987
 |title=A rigorous examination of the Chandrasekhar theory of stellar collapse
 |journal=[[The Astrophysical Journal]]
 |volume=323
 |issue=1
 |pages=140–144
 |bibcode=1987ApJ...323..140L
 |doi=10.1086/165813
 |url=https://dash.harvard.edu/handle/1/32706795
 |access-date=20 March 2020
|archive-date=3 March 2020
|archive-url=https://web.archive.org/web/20200303072644/https://dash.harvard.edu/handle/1/32706795
 |url-status=live
 }}</ref><ref name=canal1997>
{{Cite book
 |last1=Canal |first1=R.
 |last2=Gutiérrez |first2=J. L.
 |date=1997
 |chapter=The possible white dwarf-neutron star connection
 |editor1-last=Isern |editor1-first=J.
 |editor2-last=Hernanz |editor2-first=M.
 |editor3-last=Gracia-Berro |editor3-first=E.
 |title=White Dwarfs: Proceedings of the 10th European Workshop on White Dwarfs
 |series=Astrophysics and Space Science Library
 |volume=214 |page=49
 |publisher=[[Kluwer Academic Publishers]]
 |location=Dordrecht
 |arxiv=astro-ph/9701225
 |bibcode=1997ASSL..214...49C
 |doi=10.1007/978-94-011-5542-7_7
 |isbn=978-0-7923-4585-5
|s2cid=9288287
 }}</ref> and would begin to collapse. However, the current view is that this limit is not normally attained; increasing temperature and density inside the core ignite carbon fusion as the star approaches the limit (to within about 1%)<ref>
{{Cite book
 |last=Wheeler |first=J. C.
 |date=2000
 |title=Cosmic Catastrophes: Supernovae, Gamma-Ray Bursts, and Adventures in Hyperspace
 |url=https://books.google.com/books?id=s3SFQgAACAAJ
 |page=96
 |publisher=[[Cambridge University Press]]
 |isbn=978-0-521-65195-0
 |url-status=live
 |archive-url=https://web.archive.org/web/20150910190113/https://books.google.com/books?id=s3SFQgAACAAJ
 |archive-date=10 September 2015
}}</ref> before collapse is initiated.<ref name="Mazzali2007"/> In contrast, for a core primarily composed of oxygen, neon and magnesium, the collapsing white dwarf will typically form a [[neutron star]]. In this case, only a fraction of the star's mass will be ejected during the collapse.<ref name=canal1997/>

[[File:An isolated neutron star in the Small Magellanic Cloud.jpg|thumb|The blue spot at the centre of the red ring is an isolated neutron star in the [[Small Magellanic Cloud]].]]
Within a few seconds of the collapse process, a substantial fraction of the matter in the white dwarf undergoes nuclear fusion, releasing enough energy (1–{{val|2|e=44|ul=J}})<ref name="aaa270">
{{Cite journal
 |last1=Khokhlov |first1=A. M.
 |last2=Mueller |first2=E.
 |last3=Höflich |first3=P. A.
 |date=1993
 |title=Light curves of Type IA supernova models with different explosion mechanisms
 |journal=[[Astronomy and Astrophysics]]
 |volume=270 |issue=1–2 |pages=223–248
 |bibcode=1993A&A...270..223K
}}</ref> to [[gravitational binding energy|unbind]] the star in a supernova.<ref name="ropke">
{{Cite journal
 |last1=Röpke |first1=F. K.
 |last2=Hillebrandt |first2=W.
 |date=2004
 |title=The case against the progenitor's carbon-to-oxygen ratio as a source of peak luminosity variations in type Ia supernovae
 |journal=[[Astronomy and Astrophysics Letters]]
 |volume=420 |issue=1 |pages=L1–L4
 |arxiv=astro-ph/0403509
 |bibcode=2004A&A...420L...1R
 |doi=10.1051/0004-6361:20040135
|s2cid=2849060
 }}</ref> An outwardly expanding [[shock wave]] is generated, with matter reaching velocities on the order of 5,000–20,000 [[kilometers per second|km/s]], or roughly 3% of the speed of light. There is also a significant increase in luminosity, reaching an [[absolute magnitude]] of −19.3 (or 5&nbsp;billion times brighter than the Sun), with little variation.<ref name="explosion_model">
{{Cite journal
 |last1=Hillebrandt |first1=W.
 |last2=Niemeyer |first2=J. C.
 |date=2000
 |title=Type IA Supernova Explosion Models
 |journal=[[Annual Review of Astronomy and Astrophysics]]
 |volume=38 |issue=1 |pages=191–230
 |arxiv=astro-ph/0006305
 |bibcode=2000ARA&A..38..191H
 |doi=10.1146/annurev.astro.38.1.191
|s2cid=10210550
 }}</ref>

The model for the formation of this category of supernova is a close binary star system. The more massive of the two stars is the first to [[Stellar evolution|evolve]] off the [[main sequence]], and it expands to form a [[red giant]]. The two stars now share a common envelope, causing their mutual orbit to shrink. The giant star then sheds most of its envelope, losing mass until it can no longer continue [[nuclear fusion]]. At this point, it becomes a white dwarf star, composed primarily of carbon and oxygen.<ref>
{{cite conference
 |last=Paczyński |first=B.
 |date=1976
 |title=Common Envelope Binaries
 |book-title=Structure and Evolution of Close Binary Systems
 |conference=IAU Symposium No. 73
 |editor1-last=Eggleton |editor1-first=P.
 |editor2-last=Mitton |editor2-first=S.
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}}</ref> Eventually, the secondary star also evolves off the main sequence to form a red giant. Matter from the giant is accreted by the white dwarf, causing the latter to increase in mass. The exact details of initiation and of the heavy elements produced in the catastrophic event remain unclear.<ref>{{Cite journal |last1=Poludnenko |first1=Alexei Y. |last2=Chambers |first2=Jessica |last3=Ahmed |first3=Kareem |last4=Gamezo |first4=Vadim N. |last5=Taylor |first5=Brian D. |date=November 2019 |title=A unified mechanism for unconfined deflagration-to-detonation transition in terrestrial chemical systems and type Ia supernovae |url=https://www.science.org/doi/10.1126/science.aau7365 |journal=Science |language=en |volume=366 |issue=6465 |article-number=eaau7365 |bibcode=2019Sci...366.7365P |doi=10.1126/science.aau7365 |pmid=31672866 |arxiv=1911.00050 |s2cid=207817150 |issn=0036-8075 |quote=Theoretical models of SNIa have remained limited because of uncertainties in the explosion mechanisms. [...] SNIa explosions are driven by fast thermonuclear burning in <sup>12</sup>C/<sup>16</sup>O white dwarf (WD) stars with a mass close to, or below, the Chandrasekhar mass limit of ≈1.4 solar masses [...] Beyond this general statement, however, the exact mechanisms of SNIa remain unclear, with a number of possible scenarios.}}</ref>

Type Ia supernovae produce a characteristic light curve—the graph of luminosity as a function of time—after the event. This luminosity is generated by the [[radioactive decay]] of [[nickel]]-56 through [[cobalt]]-56 to [[iron]]-56.<ref name="explosion_model"/> The peak luminosity of the light curve is extremely consistent across normal Type Ia supernovae, having a maximum absolute magnitude of about −19.3. This is because typical Type Ia supernovae arise from a consistent type of progenitor star by gradual mass acquisition, and explode when they acquire a consistent typical mass, giving rise to very similar supernova conditions and behaviour. This allows them to be used as a secondary<ref>
{{Cite journal
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A second model for the formation of Type Ia supernovae involves the merger of two white dwarf stars, with the combined mass momentarily exceeding the Chandrasekhar limit.<ref>
{{cite journal
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}}</ref> This is sometimes referred to as the double-degenerate model, as both stars are degenerate white dwarfs. Due to the possible combinations of mass and chemical composition of the pair there is much variation in this type of event,<ref>
{{cite journal
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}}</ref> and, in many cases, there may be no supernova at all, in which case they will have a less luminous light curve than the more normal SN Type Ia.<ref>{{Cite journal |last1=Maoz |first1=Dan |last2=Mannucci |first2=Filippo |last3=Nelemans |first3=Gijs |date=18 August 2014 |title=Observational Clues to the Progenitors of Type Ia Supernovae |url=https://www.annualreviews.org/doi/10.1146/annurev-astro-082812-141031 |journal=Annual Review of Astronomy and Astrophysics |language=en |volume=52 |issue=1 |pages=107–170 |doi=10.1146/annurev-astro-082812-141031 |bibcode=2014ARA&A..52..107M |arxiv=1312.0628 |hdl=2066/156088 |s2cid=55533680 |issn=0066-4146}}</ref>

====Non-standard Type Ia====
Abnormally bright Type Ia supernovae occur when the white dwarf already has a mass higher than the Chandrasekhar limit,<ref>
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{{Cite journal
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 |bibcode=2010ApJ...714.1209T
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|s2cid=13990681
 }}</ref> but the ejected material will have less than normal kinetic energy. This super-Chandrasekhar-mass scenario can occur, for example, when the extra mass is supported by [[differential rotation]].<ref>{{cite journal | title=Thermonuclear explosions of rapidly differentially rotating white dwarfs: Candidates for superluminous Type Ia supernovae? | last1=Fink | first1=M. | last2=Kromer | first2=M. | last3=Hillebrandt | first3=W. | last4=Röpke | first4=F. K. | last5=Pakmor | first5=R. | last6=Seitenzahl | first6=I. R. | last7=Sim | first7=S. A. | journal=Astronomy & Astrophysics | volume=618 | id=A124 | date=October 2018 | pages=A124 | doi=10.1051/0004-6361/201833475 | arxiv=1807.10199 | bibcode=2018A&A...618A.124F | s2cid=118965737 }}</ref>

There is no formal sub-classification for non-standard Type Ia supernovae. It has been proposed that a group of sub-luminous supernovae that occur when helium accretes onto a white dwarf should be classified as '''Type Iax'''.<ref name=wang>
{{cite journal
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 |arxiv=1301.1047
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|s2cid=118612081
 }}</ref><ref name=foley>
{{cite journal
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 |year=2013
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 |arxiv=1212.2209
 |bibcode=2013ApJ...767...57F
 |doi=10.1088/0004-637X/767/1/57
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 }}</ref> This type of supernova may not always completely destroy the white dwarf progenitor and could leave behind a [[zombie star]].<ref name="mccully">
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 |year=2014
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 |journal=[[Nature (journal)|Nature]]
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 |arxiv=1408.1089
 |bibcode=2014Natur.512...54M
 |doi=10.1038/nature13615
 |pmid=25100479
|s2cid=4464556
 }}</ref>

One specific type of supernova originates from exploding white dwarfs, like Type Ia, but contains hydrogen lines in their spectra, possibly because the white dwarf is surrounded by an envelope of hydrogen-rich [[Circumstellar disc|circumstellar material]]. These supernovae have been dubbed '''Type Ia/IIn''', '''Type Ian''', '''Type IIa''' and '''Type IIan'''.<ref>
{{cite journal
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 |year=2013
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 |arxiv=1304.0763
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|s2cid=51415846
 }}</ref>

The quadruple star [[HD 74438]], belonging to the open cluster [[IC 2391]] the [[Vela constellation]], has been predicted to become a non-standard Type Ia supernova.<ref name="GIAISURVEY">{{cite journal |last1=Gilmore |first1=Gerry |last2=Randich |first2=Sofia |title=The Gaia-ESO Public Spectroscopic Survey |journal=The Messenger |date=March 2012 |volume=147 |issue=147 |pages=25–31 |publisher=European Southern Observatory |location=Garching, Germany |language=en |bibcode=2012Msngr.147...25G}}</ref><ref name="supernova">{{cite journal |last1=Merle |first1=Thibault |last2=Hamers |first2=Adrian S. |last3=Van Eck |first3=Sophie |last4=Jorissen |first4=Alain |last5=Van der Swaelmen |first5=Mathieu |last6=Pollard |first6=Karen |last7=Smiljanic |first7=Rodolfo |last8=Pourbaix |first8=Dimitri |last9=Zwitter |first9=Tomaž |last10=Traven |first10=Gregor |last11=Gilmore |first11=Gerry |last12=Randich |first12=Sofia |last13=Gonneau |first13=Anaïs |last14=Hourihane |first14=Anna |last15=Sacco |first15=Germano |last16=Worley |first16=C. Clare |title=A spectroscopic quadruple as a possible progenitor of sub-Chandrasekhar type Ia supernovae |journal=Nature Astronomy |date=12 May 2022 |volume=6 |issue=6 |pages=681–688 |doi=10.1038/s41550-022-01664-5|arxiv=2205.05045 |bibcode=2022NatAs...6..681M |s2cid=248665714 }}</ref>

===Core collapse===
[[Image:Evolved star fusion shells.svg|thumb|The layers of a massive, evolved star just before core collapse (not to scale).]]
Very massive stars can undergo core collapse when nuclear fusion becomes unable to sustain the core against its own gravity; passing this threshold is the cause of all types of supernova except Type Ia. The collapse may cause violent expulsion of the outer layers of the star resulting in a supernova. However, if the release of gravitational potential energy is insufficient, the star may instead collapse into a [[black hole]] or [[neutron star]] with little radiated energy.<ref name="heger"/> 

Core collapse can be caused by several different mechanisms: exceeding the [[Chandrasekhar limit]]; [[electron capture]]; [[Pair-instability supernova|pair-instability]]; or [[photodisintegration]].<ref name="heger">
{{Cite journal
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* When a massive star develops an iron core larger than the Chandrasekhar mass it will no longer be able to support itself by [[electron degeneracy pressure]] and will collapse further to a neutron star or black hole.
* Electron capture by magnesium in a [[degenerate matter|degenerate]] O/Ne/Mg core (8–10 solar mass progenitor star) removes support and causes [[gravitational collapse]] followed by explosive oxygen fusion, with very similar results.
* Electron-positron pair production in a large post-helium burning core removes thermodynamic support and causes initial collapse followed by runaway fusion, resulting in a pair-instability supernova.
* A sufficiently large and hot [[stellar core]] may generate gamma-rays energetic enough to initiate photodisintegration directly, which will cause a complete collapse of the core.

The table below lists the known reasons for core collapse in massive stars, the types of stars in which they occur, their associated supernova type, and the remnant produced. The [[metallicity]] is the proportion of elements other than hydrogen or helium, as compared to the Sun. The initial mass is the mass of the star prior to the supernova event, given in multiples of the Sun's mass, although the mass at the time of the supernova may be much lower.<ref name="heger"/>

Type IIn supernovae are not listed in the table. They can be produced by various types of core collapse in different progenitor stars, possibly even by Type Ia white dwarf ignitions, although it seems that most will be from iron core collapse in luminous [[supergiant]]s or [[hypergiant]]s (including LBVs). The narrow spectral lines for which they are named occur because the supernova is expanding into a small dense cloud of circumstellar material.<ref name="moriya">
{{cite journal
 |last1=Moriya |first1=T. J.
 |date=2012
 |title=Progenitors of Recombining Supernova Remnants
 |journal=[[The Astrophysical Journal]]
 |volume=750 |issue=1 |pages=L13
 |arxiv=1203.5799
 |bibcode=2012ApJ...750L..13M
 |doi=10.1088/2041-8205/750/1/L13
|s2cid=119209527
 }}</ref> It appears that a significant proportion of supposed Type IIn supernovae are supernova impostors, massive eruptions of LBV-like stars similar to the Great Eruption of [[Eta Carinae]]. In these events, material previously ejected from the star creates the narrow absorption lines and causes a shock wave through interaction with the newly ejected material.<ref name="smith">
{{Cite journal
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 }}</ref>

{|class="wikitable"
|+ Core collapse scenarios by mass and metallicity<ref name="heger"/>
|-
! Cause of collapse !! Progenitor star approximate initial mass ([[solar mass]]es) !! Supernova type !! Remnant
|-
| [[Electron capture supernova|Electron capture in a degenerate O+Ne+Mg core]] || 9–10 || Faint II-P ||Neutron star
|-
|rowspan="7"| Iron core collapse || 10–25 || Faint II-P || Neutron star
|-
| 25–40 with low or solar metallicity || Normal II-P || Black hole after fallback of material onto an initial neutron star
|-
| 25–40 with very high metallicity || II-L or II-b || Neutron star
|-
| 40–90 with low metallicity || None || Black hole
|-
| ≥&nbsp;40 with near-solar metallicity || Faint Ib/c, or [[hypernova]] with [[gamma-ray burst]] (GRB) || Black hole after fallback of material onto an initial neutron star
|-
| ≥&nbsp;40 with very high metallicity || Ib/c || Neutron star
|-
| ≥&nbsp;90 with low metallicity || None, possible GRB || Black hole
|-
| Pair instability{{anchor|type_II_P_anchor}} || 140–250 with low metallicity || II-P, sometimes a hypernova, possible GRB || No remnant
|-
| Photodisintegration || ≥&nbsp;250 with low metallicity || None (or luminous supernova?), possible GRB || Massive black hole
|}

====Detailed process====
[[Image:Core collapse scenario.svg|upright=1.4|thumb|Within a massive, evolved star (a) the onion-layered shells of elements undergo fusion, forming an iron core (b) that reaches Chandrasekhar-mass and starts to collapse. The inner part of the core is compressed into neutrons (c), causing infalling material to bounce (d) and form an outward-propagating shock front (red). The shock starts to stall (e), but it is re-invigorated, likely by [[Supernova neutrinos|neutrino heating]]. The surrounding material is blasted away (f), leaving only a degenerate remnant.<ref name="Janka-2007"/>]]

When a stellar core is no longer supported against gravity, it collapses in on itself with velocities reaching 70,000&nbsp;km/s (0.23[[Speed of light|''c'']]),<ref name="grav_waves">
{{cite journal
 |last1=Fryer |first1=C. L.
 |last2=New |first2=K. C. B.
 |year=2003
 |title=Gravitational Waves from Gravitational Collapse
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 |volume=6 |issue=1|page=2
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 |bibcode=2003LRR.....6....2F
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}}</ref> resulting in a rapid increase in temperature and density. What follows depends on the mass and structure of the collapsing core, with low-mass degenerate cores forming neutron stars, higher-mass degenerate cores mostly collapsing completely to black holes, and non-degenerate cores undergoing runaway fusion.<ref name="Janka-2007"/><ref name="Hurley-2000">{{Cite journal |last1=Hurley |first1=J. R. |last2=Pols |first2=O. R. |last3=Tout |first3=C. A. |date=1 July 2000 |title=Comprehensive analytic formulae for stellar evolution as a function of mass and metallicity |doi-access=free |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=315 |issue=3 |pages=543–569 |doi=10.1046/j.1365-8711.2000.03426.x |bibcode=2000MNRAS.315..543H |arxiv=astro-ph/0001295 |issn=0035-8711}}</ref>

The initial collapse of degenerate cores is accelerated by [[beta decay]], photodisintegration and electron capture, which causes a burst of [[electron neutrino]]s. As the density increases, [[Supernova neutrinos|neutrino emission]] is cut off as they become trapped in the core. The inner core eventually reaches typically 30&nbsp;[[kilometre|km]] in diameter<ref name="WoosleyJanka"/> with a density comparable to that of an [[atomic nucleus]], and neutron [[degeneracy pressure]] tries to halt the collapse. If the core mass is more than about 15 solar masses then neutron degeneracy is insufficient to stop the collapse and a black hole forms directly with no supernova.<ref name=renzon2018/>

In lower mass cores the collapse is stopped and the newly formed neutron core has an initial temperature of about 100&nbsp;billion [[kelvin]]s, 6,000 times the temperature of the [[Sun's core]].<ref name="Janka-2007">
{{Cite journal
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|s2cid=15819376
 }}</ref> At this temperature, neutrino-antineutrino pairs of all [[Neutrino oscillation|flavours]] are efficiently formed by [[Thermal radiation|thermal emission]]. These thermal neutrinos are several times more abundant than the electron-capture neutrinos.<ref>
{{Cite book
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}}</ref> About 10<sup>46</sup> joules, approximately 10% of the star's rest mass, is converted into a ten-second burst of neutrinos, which is the main output of the event.<ref name="WoosleyJanka"/><ref name="barwick">
{{Cite journal
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}}</ref> The suddenly halted core collapse rebounds and produces a shock wave that stalls in the outer core within milliseconds<ref>
{{Cite journal
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 }}</ref> as energy is lost through the dissociation of heavy elements. A process that is {{As of|2023|alt=not clearly understood}} is necessary to allow the outer layers of the core to reabsorb around 10<sup>44</sup> joules<ref name="barwick"/> (1 [[Foe (unit)|foe]]) from the [[Supernova neutrinos|neutrino pulse]], producing the visible brightness, although there are other theories that could power the explosion.<ref name="WoosleyJanka"/>

Some material from the outer envelope falls back onto the neutron star, and, for cores beyond about {{Solar mass|8}}, there is sufficient fallback to form a black hole. This fallback will reduce the kinetic energy created and the mass of expelled radioactive material, but in some situations, it may also generate [[relativistic jet]]s that result in a [[gamma-ray burst]] or an exceptionally luminous supernova.<ref name=piram2019>{{cite journal |bibcode=2019ApJ...871L..25P |title=Relativistic Jets in Core-collapse Supernovae |last1=Piran |first1=Tsvi |last2=Nakar |first2=Ehud |last3=Mazzali |first3=Paolo |last4=Pian |first4=Elena |journal=The Astrophysical Journal |year=2019 |volume=871 |issue=2 |pages=L25 |doi=10.3847/2041-8213/aaffce |s2cid=19266567 |doi-access=free |arxiv=1704.08298 }}</ref>

The collapse of a massive non-degenerate core will ignite further fusion.<ref name="Hurley-2000"/> When the core collapse is initiated by [[Pair-instability supernova|pair instability]] ([[photon]]s turning into [[electron]]-[[positron]] pairs, thereby reducing the radiation pressure) oxygen fusion begins and the collapse may be halted. For core masses of {{Solar mass|40–60}}, the collapse halts and the star remains intact, but collapse will occur again when a larger core has formed. For cores of around {{Solar mass|60–130}}, the fusion of oxygen and heavier elements is so energetic that the entire star is disrupted, causing a supernova. At the upper end of the mass range, the supernova is unusually luminous and extremely long-lived due to many solar masses of ejected <sup>56</sup>Ni. For even larger core masses, the core temperature becomes high enough to allow photodisintegration and the core collapses completely into a black hole.<ref name="kasen">
{{Cite journal
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====Type II====
{{Main|Type II supernova}}
[[Image:SN 1997D.jpg|thumb|The atypical subluminous Type II [[SN 1997D]]]]
Stars with initial masses less than about {{Solar mass|8}} never develop a core large enough to collapse and they eventually lose their atmospheres to become white dwarfs. Stars with at least {{Solar mass|9}} (possibly as much as {{Solar mass|12}}<ref name="superagb">
{{Cite journal
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 }}</ref>) evolve in a complex fashion, progressively burning heavier elements at hotter temperatures in their cores.<ref name="WoosleyJanka">
{{Cite journal
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{{cite journal
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 |volume=304 |issue=5679 |pages=1915–1916
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 }}</ref> The star becomes layered like an onion, with the burning of more easily fused elements occurring in larger shells.<ref name=heger/><ref name="hinshaw">
{{cite book
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}}</ref> Although popularly described as an onion with an iron core, the least massive supernova progenitors only have oxygen-[[neon]](-[[magnesium]]) cores. These [[super-AGB star]]s may form the majority of core collapse supernovae, although less luminous and so less commonly observed than those from more massive progenitors.<ref name="superagb"/>

If core collapse occurs during a supergiant phase when the star still has a hydrogen envelope, the result is a Type II supernova.<ref name=Horiuchi_et_al_2014>{{cite journal |bibcode=2014MNRAS.445L..99H |arxiv=1409.0006 |doi=10.1093/mnrasl/slu146|title=The red supergiant and supernova rate problems: Implications for core-collapse supernova physics |year=2014 |last1=Horiuchi |first1=S. |last2=Nakamura |first2=K. |last3=Takiwaki |first3=T. |last4=Kotake |first4=K. |last5=Tanaka |first5=M. |journal=Monthly Notices of the Royal Astronomical Society: Letters |volume=445 |pages=L99–L103 |doi-access=free }}</ref> The rate of mass loss for luminous stars depends on the metallicity and [[luminosity]]. Extremely luminous stars at near solar metallicity will lose all their hydrogen before they reach core collapse and so will not form a supernova of Type II.<ref name=Horiuchi_et_al_2014/> At low metallicity, all stars will reach core collapse with a hydrogen envelope but sufficiently massive stars collapse directly to a black hole without producing a visible supernova.<ref name="heger"/>

Stars with an initial mass up to about 90 times the Sun, or a little less at high metallicity, result in a Type II-P supernova, which is the most commonly observed type. At moderate to high metallicity, stars near the upper end of that mass range will have lost most of their hydrogen when core collapse occurs and the result will be a Type II-L supernova.<ref>{{cite journal |doi=10.1093/mnras/stu1760 |bibcode=2014MNRAS.445..554F |arxiv=1409.1536 |title=A sample of Type II-L supernovae |year=2014 |last1=Faran |first1=T. |last2=Poznanski |first2=D. |last3=Filippenko |first3=A. V. |last4=Chornock |first4=R. |last5=Foley |first5=R. J. |last6=Ganeshalingam |first6=M. |last7=Leonard |first7=D. C. |last8=Li |first8=W. |last9=Modjaz |first9=M. |last10=Serduke |first10=F. J. D. |last11=Silverman |first11=J. M. |journal=Monthly Notices of the Royal Astronomical Society |volume=445 |issue=1 |pages=554–569 |doi-access=free }}</ref> At very low metallicity, stars of around {{Solar mass|140–250}} will reach core collapse by pair instability while they still have a hydrogen atmosphere and an oxygen core and the result will be a supernova with Type II characteristics but a very large mass of ejected <sup>56</sup>Ni and high luminosity.<ref name="heger"/><ref>{{cite journal|title=Mind the Gap: The Location of the Lower Edge of the Pair-instability Supernova Black Hole Mass Gap |first1=R. |last1=Farmer |first2=M. |last2=Renzo |first3=S. E. |last3=de Mink |first4=P. |last4=Marchant |first5=S. |last5=Justham |doi=10.3847/1538-4357/ab518b |bibcode=2019ApJ...887...53F |arxiv=1910.12874 |journal=The Astrophysical Journal |year=2019 |volume=887 |number=1 |page=53 |doi-access=free }}</ref>

====Type Ib and Ic====
{{Main|Type Ib and Ic supernovae}}
[[Image:Supernova 2008D.jpg|thumb|upright=1.2|Type Ib SN 2008D<ref>
{{cite journal
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 }}</ref> at the far upper end of the galaxy, shown in [[X-ray]] (left) and visible light (right),<ref>
{{cite journal
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 |last2=Nakar |first2=E.
 |year=2014
 |title=Sn 2008D: A Wolf-Rayet Explosion Through a Thick Wind
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 }}</ref> with the brighter SN 2007uy closer to the centre]]

These supernovae, like those of Type II, are massive stars that undergo core collapse. Unlike the progenitors of Type II supernovae, the stars which become Type Ib and Type Ic supernovae have lost most of their outer (hydrogen) envelopes due to strong [[stellar wind]]s or else from interaction with a companion.<ref>
{{cite conference
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}}</ref> These stars are known as [[Wolf–Rayet stars]], and they occur at moderate to high metallicity where continuum driven winds cause sufficiently high mass-loss rates. Observations of Type Ib/c supernova do not match the observed or expected occurrence of Wolf–Rayet stars. Alternate explanations for this type of core collapse supernova involve stars stripped of their hydrogen by binary interactions. Binary models provide a better match for the observed supernovae, with the proviso that no suitable binary helium stars have ever been observed.<ref name="eldridge">
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Type Ib supernovae are the more common and result from Wolf–Rayet stars of [[Wolf-Rayet star#Classification|type WC]] which still have helium in their atmospheres. For a narrow range of masses, stars evolve further before reaching core collapse to become [[Wolf-Rayet star#Classification|WO stars]] with very little helium remaining, and these are the progenitors of Type Ic supernovae.<ref>{{cite journal |doi=10.1093/mnras/stx1496|title=Towards a better understanding of the evolution of Wolf–Rayet stars and Type Ib/Ic supernova progenitors |year=2017 |last1=Yoon |first1=Sung-Chul |journal=Monthly Notices of the Royal Astronomical Society |volume=470 |issue=4 |pages=3970–3980 |doi-access=free |arxiv=1706.04716 |bibcode=2017MNRAS.470.3970Y }}</ref>

A few percent of the Type Ic supernovae are associated with [[gamma-ray burst]]s (GRB), though it is also believed that any hydrogen-stripped Type Ib or Ic supernova could produce a GRB, depending on the circumstances of the geometry.<ref>
{{Cite journal
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 }}</ref> The mechanism for producing this type of GRB is the jets produced by the magnetic field of the rapidly spinning [[magnetar]] formed at the collapsing core of the star. The jets would also transfer energy into the expanding outer shell, producing a [[super-luminous supernova]].<ref name=piram2019/><ref>
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Ultra-stripped supernovae occur when the exploding star has been stripped (almost) all the way to the metal core, via mass transfer in a close binary.<ref>
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 | doi=10.1093/mnras/stv990 | doi-access=free }}</ref> As a result, very little material is ejected from the exploding star (c. {{solar mass|0.1}}). In the most extreme cases, ultra-stripped supernovae can occur in naked metal cores, barely above the Chandrasekhar mass limit. SN 2005ek<ref>
{{cite journal
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 |s2cid=118690361 }}</ref> might be the first observational example of an ultra-stripped supernova, giving rise to a relatively dim and fast decaying light curve. The nature of ultra-stripped supernovae can be both iron core-collapse and electron capture supernovae, depending on the mass of the collapsing core. Ultra-stripped supernovae are believed to be associated with the second supernova explosion in a binary system, producing for example a tight double neutron star system.<ref name="TaurisKramerFreire2017">{{cite journal | last1 = Tauris | first1 = T. M. | last2 = Kramer | first2 = M. | last3 = Freire | first3 = P. C. C. | last4 = Wex | first4 = N. | last5 = Janka | first5 = H.-T. | last6 = Langer | first6 = N. | last7 = Podsiadlowski | first7 = Ph. | last8 = Bozzo | first8 = E. | last9 = Chaty | first9 = S. | last10 = Kruckow | first10 = M. U. | last11 = Heuvel | first11 = E. P. J. van den | last12 = Antoniadis | first12 = J. | last13 = Breton | first13 = R. P. | last14 = Champion | first14 = D. J. | title = Formation of Double Neutron Star Systems | journal = The Astrophysical Journal | date = 13 September 2017 | volume = 846 | issue = 2 | page = 170 | eissn = 1538-4357 | doi = 10.3847/1538-4357/aa7e89 | arxiv = 1706.09438 | bibcode = 2017ApJ...846..170T | s2cid = 119471204 | doi-access = free }}</ref><ref name="DeKasliwalOfek2018">{{cite journal | last1 = De | first1 = K. | last2 = Kasliwal | first2 = M. M. |author2-link=Mansi Kasliwal| last3 = Ofek | first3 = E. O. | last4 = Moriya | first4 = T. J. | last5 = Burke | first5 = J. | last6 = Cao | first6 = Y. | last7 = Cenko | first7 = S. B. | last8 = Doran | first8 = G. B. | last9 = Duggan | first9 = G. E. | last10 = Fender | first10 = R. P. | last11 = Fransson | first11 = C. | last12 = Gal-Yam | first12 = A. | last13 = Horesh | first13 = A. | last14 = Kulkarni | first14 = S. R. | last15 = Laher | first15 = R. R. | last16 = Lunnan | first16 = R. | last17 = Manulis | first17 = I. | last18 = Masci | first18 = F. | last19 = Mazzali | first19 = P. A. | last20 = Nugent | first20 = P. E. | last21 = Perley | first21 = D. A. | last22 = Petrushevska | first22 = T. | last23 = Piro | first23 = A. L. | last24 = Rumsey | first24 = C. | last25 = Sollerman | first25 = J. | last26 = Sullivan | first26 = M. | last27 = Taddia | first27 = F. | title = A hot and fast ultra-stripped supernova that likely formed a compact neutron star binary | journal = Science | date = 12 October 2018 | volume = 362 | issue = 6411 | pages = 201–206 | issn = 0036-8075 | eissn = 1095-9203 | doi = 10.1126/science.aas8693 | pmid = 30309948 | arxiv = 1810.05181 | bibcode = 2018Sci...362..201D | s2cid = 52961306 | url = }}</ref>

In 2022 a team of astronomers led by researchers from the Weizmann Institute of Science reported the first supernova explosion showing direct evidence for a Wolf-Rayet progenitor star. [[SN 2019hgp]] was a Type Icn supernova and is also the first in which the element neon has been detected.<ref>{{cite journal |doi=10.1038/s41586-021-04155-1 |title=A WC/WO star exploding within an expanding carbon–oxygen–neon nebula |year=2022 |last1=Gal-Yam |first1=A. |last2=Bruch |first2=R. |last3=Schulze |first3=S. |last4=Yang |first4=Y. |last5=Perley |first5=D. A. |last6=Irani |first6=I. |last7=Sollerman |first7=J. |last8=Kool |first8=E. C. |last9=Soumagnac |first9=M. T. |last10=Yaron |first10=O. |last11=Strotjohann |first11=N. L. |last12=Zimmerman |first12=E. |last13=Barbarino |first13=C. |last14=Kulkarni |first14=S. R. |last15=Kasliwal |first15=M. M. |author15-link=Mansi Kasliwal|last16=De |first16=K. |last17=Yao |first17=Y. |last18=Fremling |first18=C. |last19=Yan |first19=L. |last20=Ofek |first20=E. O. |last21=Fransson |first21=C. |last22=Filippenko |first22=A. V. |last23=Zheng |first23=W. |last24=Brink |first24=T. G. |last25=Copperwheat |first25=C. M. |last26=Foley |first26=R. J. |last27=Brown |first27=J. |last28=Siebert |first28=M. |last29=Leloudas |first29=G. |last30=Cabrera-Lavers |first30=A. L. |journal=Nature |volume=601 |issue=7892 |pages=201–204 |pmid=35022591 |arxiv=2111.12435 |bibcode=2022Natur.601..201G |s2cid=244527654 }}</ref><ref>{{Cite web|title=Astronomers discover first supernova explosion of a Wolf-Rayet star|url=https://www.iac.es/en/outreach/news/astronomers-discover-first-supernova-explosion-wolf-rayet-star|access-date=9 February 2022|website=Instituto de Astrofísica de Canarias • IAC|date=12 January 2022 |language=en}}</ref>

====<span class="anchor" id="Electron-capture supernovae"></span> Electron-capture supernovae ====
In 1980, a "third type" of supernova was predicted by [[Ken'ichi Nomoto]] of the [[University of Tokyo]], called an electron-capture supernova. It would arise when a star "in the transitional range (~8 to 10 solar masses) between white dwarf formation and iron core-collapse supernovae", and with a [[degenerate matter|degenerate]] O+Ne+Mg core,<ref name=HowellEtAl2021-01a/> imploded after its core ran out of nuclear fuel, causing gravity to compress the electrons in the star's core into their atomic nuclei,<ref name=KeckObsNews2021-06-28-01a/><ref name=RTE2021-06-28-01a/> leading to a supernova explosion and leaving behind a neutron star.<ref name="heger"/> In June 2021, a paper in the journal ''[[Nature Astronomy]]'' reported that the 2018 supernova [[SN 2018zd]] (in the galaxy [[NGC 2146]], about 31 million light-years from [[Earth]]) appeared to be the first observation of an electron-capture supernova.<ref name=HowellEtAl2021-01a>{{cite journal |author1=Hiramatsu D |author2=Howell D |author3=Van S |display-authors=etal |date=28 June 2021 |title=The electron-capture origin of supernova 2018zd |url=https://www.nature.com/articles/s41550-021-01384-2 |journal=Nat Astron |volume=5 |issue=9 |pages=903–910 |doi=10.1038/s41550-021-01384-2 |arxiv=2011.02176 |bibcode=2021NatAs...5..903H |s2cid=226246044 |access-date=1 July 2021 |archive-date=30 June 2021 |archive-url=https://web.archive.org/web/20210630023436/https://www.nature.com/articles/s41550-021-01384-2 |url-status=live }}</ref><ref name=KeckObsNews2021-06-28-01a>{{cite web |url=https://keckobservatory.org/electron-capture-supernova |title=New, Third Type Of Supernova Observed |date=28 June 2021 |website=[[W. M. Keck Observatory]] |access-date=1 July 2021 |archive-date=29 June 2021 |archive-url=https://web.archive.org/web/20210629155228/https://www.keckobservatory.org/electron-capture-supernova |url-status=live }}</ref><ref name=RTE2021-06-28-01a>{{cite news|url=https://www.rte.ie/news/newslens/2021/0628/1231824-supernova-crab-nebula/|title=Astronomers discover new type of supernova|publisher=[[RTE News]]|author=|agency=[[Press Association|PA]]|date=28 June 2021|access-date=1 July 2021|quote=In 1980, Ken'ichi Nomoto of the University of Tokyo predicted a third type called an electron capture supernova. ... In an electron capture supernova, as the core runs out of fuel, gravity forces electrons in the core into their atomic nuclei, causing the star to collapse in on itself.|archive-date=30 June 2021|archive-url=https://web.archive.org/web/20210630165238/https://www.rte.ie/news/newslens/2021/0628/1231824-supernova-crab-nebula/|url-status=live}}</ref> The 1054 supernova explosion that created the Crab Nebula in our galaxy had been thought to be the best candidate for an electron-capture supernova, and the 2021 paper makes it more likely that this was correct.<ref name=KeckObsNews2021-06-28-01a/><ref name=RTE2021-06-28-01a/>

===Failed supernovae===
{{main|Failed supernova}}
The core collapse of some massive stars may not result in a visible supernova. This happens if the initial core collapse cannot be reversed by the mechanism that produces an explosion, usually because the core is too massive. These events are difficult to detect, but large surveys have detected possible candidates.<ref name=failed>
{{cite journal
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 |last2=Fraser |first2=M.
 |last3=Gilmore |first3=G.
 |year=2015
 |title=Gone without a bang: an archival HST survey for disappearing massive stars
 |journal=Monthly Notices of the Royal Astronomical Society
 |volume=453 |issue=3 |pages=2886–2901
 |arxiv=1507.05823
 |bibcode=2015MNRAS.453.2885R
 |doi=10.1093/mnras/stv1809
|doi-access=free
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 }}</ref><ref name=gerke>
{{cite journal
 |last1=Gerke |first1=J. R.
 |last2=Kochanek |first2=C. S.
 |last3=Stanek |first3=K. Z.
 |year=2015
 |title=The search for failed supernovae with the Large Binocular Telescope: first candidates
 |journal=Monthly Notices of the Royal Astronomical Society
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 |arxiv=1411.1761
 |bibcode=2015MNRAS.450.3289G
 |doi=10.1093/mnras/stv776
|doi-access=free
 |s2cid=119212331
 }}</ref> The red supergiant [[N6946-BH1]] in [[NGC 6946]] underwent a modest outburst in March 2009, before fading from view. Only a faint [[infrared]] source remains at the star's location.<ref name=adams/>

===Light curves===
[[Image:Comparative supernova type light curves.png|upright=1.75|thumb|Typical light curves for several types of supernovae; in practice, magnitude and duration varies within each type. See Karttunen et al. for Type Ia, Ib, II-L and II-P;<ref name="Springer-2016">{{cite book|editor-first1=H. |editor-last1=Karttunen |editor-first2=P. |editor-last2=Kröger |editor-first3=H. |editor-last3=Oja |editor-first4=M. |editor-last4=Poutanen |editor-first5=K. J. |editor-last5=Donner |title=Fundamental Astronomy |publisher=Springer |isbn=978-3-662-53044-3 |page=309 |year=2016}}</ref> Modjaz et al. for Type Ic and IIb;<ref name="Modjaz-2019">{{cite journal|first1=M. |last1=Modjaz |first2=C. P. |last2=Gutiérrez |first3=I. |last3=Arcavi |title=New regimes in the observation of core-collapse supernovae |journal=Nature Astronomy |doi=10.1038/s41550-019-0856-2 |volume=3 |date=August 2019 |issue=8 |pages=717–724|arxiv=1908.02476 |bibcode=2019NatAs...3..717M |s2cid=199472802 }}</ref> and Nyholm et al. for Type IIn.<ref name="Nyholm-2020">{{cite journal|first1=A. |last1=Nyholm |display-authors=etal |title=Type IIn supernova light-curve properties measured from an untargeted survey sample |journal=Astronomy and Astrophysics |doi=10.1051/0004-6361/201936097 |volume=637 |year=2020 |page=A73|arxiv=1906.05812 |bibcode=2020A&A...637A..73N |s2cid=189762490 }}</ref>]]
The ejecta gases would dim quickly without some energy input to keep them hot. The source of this energy—which can maintain the optical supernova glow for months—was, at first, a puzzle. Some considered rotational energy from the central pulsar as a source.<ref>{{Cite journal |last1=Michel |first1=F. Curtis |last2=Kennel |first2=C. F. |last3=Fowler |first3=William A. |date=1987-11-13 |title=When Will a Pulsar in Supernova 1987a Be Seen? |journal=Science |volume=238 |issue=4829 |pages=938–940 |doi=10.1126/science.238.4829.938|pmid=17829358 |bibcode=1987Sci...238..938M |s2cid=46408677 }}</ref> Although the energy that initially powers each type of supernovae is delivered promptly, the light curves are dominated by subsequent radioactive heating of the rapidly expanding ejecta. The intensely radioactive nature of the ejecta gases was first calculated on sound nucleosynthesis grounds in the late 1960s, and this has since been demonstrated as correct for most supernovae.<ref>{{cite journal
 |last1=Bodansky
 |first1=D.
 |last2=Clayton
 |first2=D. D.
 |last3=Fowler
 |first3=W. A.
 |year=1968
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 |url-status=live
 }}</ref> It was not until [[SN 1987A]] that direct observation of gamma-ray lines unambiguously identified the major radioactive nuclei.<ref name="S.M. Matz, G.H. Share 1988">
{{cite journal
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It is now known by direct observation that much of the light curve (the graph of luminosity as a function of time) after the occurrence of a [[Type II Supernova]], such as SN 1987A, is explained by those predicted radioactive decays.<ref name=":0"/> Although the luminous emission consists of optical photons, it is the radioactive power absorbed by the ejected gases that keeps the remnant hot enough to radiate light. The radioactive decay of <sup>56</sup>Ni through its daughters <sup>56</sup>Co to <sup>56</sup>Fe produces gamma-ray [[photon]]s, primarily with energies of {{val|847|ul=keV}} and {{val|1238|u=keV|fmt=commas}}, that are absorbed and dominate the heating and thus the luminosity of the ejecta at intermediate times (several weeks) to late times (several months).<ref>
{{cite journal
 |last1=Kasen |first1=D.
 |last2=Woosley |first2=S. E.
 |year=2009
 |title=Type II Supernovae: Model Light Curves and Standard Candle Relationships
 |journal=The Astrophysical Journal
 |volume=703 |issue=2 |page=2205
 |arxiv=0910.1590
 |bibcode=2009ApJ...703.2205K
 |doi=10.1088/0004-637X/703/2/2205
|s2cid=42058638
 }}</ref> Energy for the peak of the light curve of SN1987A was provided by the decay of [[Isotopes of nickel|<sup>56</sup>Ni]] to <sup>56</sup>Co (half-life 6 days) while energy for the later light curve in particular fit very closely with the 77.3-day half-life of [[Isotopes of cobalt|<sup>56</sup>Co]] decaying to <sup>56</sup>Fe. Later measurements by space gamma-ray telescopes of the small fraction of the <sup>56</sup>Co and <sup>57</sup>Co gamma rays that escaped the SN 1987A remnant without absorption confirmed earlier predictions that those two radioactive nuclei were the power sources.<ref name="S.M. Matz, G.H. Share 1988"/>

[[File:Messier 61 with SN2020jfo (Supernova).jpg|thumb|upright=1.2|[[Messier 61]] with supernova SN2020jfo, taken by an amateur astronomer in 2020]]
The late-time decay phase of visual light curves for different supernova types all depend on radioactive heating, but they vary in shape and amplitude because of the underlying mechanisms, the way that visible radiation is produced, the epoch of its observation, and the transparency of the ejected material.<ref>{{cite journal |doi=10.1051/0004-6361/201527931 |title=A two-component model for fitting light curves of core-collapse supernovae |year=2016 |last1=Nagy |first1=A. P. |last2=Vinkó |first2=J. |journal=Astronomy & Astrophysics |volume=589 |pages=A53 |arxiv=1602.04001 |bibcode=2016A&A...589A..53N |s2cid=53380594 }}</ref> The light curves can be significantly different at other wavelengths. For example, at ultraviolet wavelengths there is an early extremely luminous peak lasting only a few hours corresponding to the breakout of the shock launched by the initial event, but that breakout is hardly detectable optically.<ref>{{Cite journal |last1=Tominaga |first1=N. |last2=Blinnikov |first2=S. |last3=Baklanov |first3=P. |last4=Morokuma |first4=T. |last5=Nomoto |first5=K. |last6=Suzuki |first6=T. |date=1 November 2009 |title=Properties of Type II Plateau Supernova SNLS-04D2dc: Multicolor Light Curves of Shock Breakout and Plateau |doi-access=free |journal=The Astrophysical Journal |volume=705 |issue=1 |pages=L10–L14 |bibcode=2009ApJ...705L..10T |arxiv=0908.2162 |doi=10.1088/0004-637X/705/1/L10 |issn=0004-637X}}</ref><ref>{{Cite journal |last1=de la Rosa |first1=Janie |last2=Roming |first2=Pete |last3=Pritchard |first3=Tyler |last4=Fryer |first4=Chris |date=22 March 2016 |title=Characterizing Mid-Ultraviolet to Optical Light Curves of Nearby Type IIn Supernovae |doi-access=free |journal=The Astrophysical Journal |volume=820 |issue=1 |page=74 |bibcode=2016ApJ...820...74D |doi=10.3847/0004-637X/820/1/74 |issn=1538-4357|hdl=1959.3/416659 |hdl-access=free }}</ref>

The light curves for Type Ia are mostly very uniform, with a consistent maximum absolute magnitude and a relatively steep decline in luminosity. Their optical energy output is driven by radioactive decay of ejected nickel-56 (half-life 6 days), which then decays to radioactive cobalt-56 (half-life 77 days). These radioisotopes excite the surrounding material to incandescence.<ref name="explosion_model"/> Modern studies of cosmology rely on <sup>56</sup>Ni radioactivity providing the energy for the optical brightness of supernovae of Type Ia, which are the "standard candles" of cosmology but whose diagnostic {{val|847|u=keV}} and {{val|1238|u=keV|fmt=commas}} gamma rays were first detected only in 2014.<ref>
{{cite journal
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 |bibcode=2014Natur.512..406C
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 }}</ref> The initial phases of the light curve decline steeply as the effective size of the [[photosphere]] decreases and trapped electromagnetic radiation is depleted. The light curve continues to decline in the [[UBV photometric system|B band]] while it may show a small shoulder in the visual at about 40 days, but this is only a hint of a secondary maximum that occurs in the infra-red as certain ionised heavy elements recombine to produce infra-red radiation and the ejecta become transparent to it. The visual light curve continues to decline at a rate slightly greater than the decay rate of the radioactive cobalt (which has the longer half-life and controls the later curve), because the ejected material becomes more diffuse and less able to convert the high energy radiation into visual radiation. After several months, the light curve changes its decline rate again as [[positron emission]] from the remaining cobalt-56 becomes dominant, although this portion of the light curve has been little-studied.<ref name=taubenberger2009>{{cite journal |doi=10.1111/j.1365-2966.2009.15478.x |title=Late-time supernova light curves: The effect of internal conversion and Auger electrons |year=2009 |last1=Seitenzahl |first1=I. R. |last2=Taubenberger |first2=S. |last3=Sim |first3=S. A. |journal=Monthly Notices of the Royal Astronomical Society |volume=400 |issue=1 |pages=531–535 |doi-access=free |arxiv=0908.0247 |bibcode=2009MNRAS.400..531S |s2cid=10283901 }}</ref>

Type Ib and Ic light curves are similar to Type Ia although with a lower average peak luminosity. The visual light output is again due to radioactive decay being converted into visual radiation, but there is a much lower mass of the created nickel-56. The peak luminosity varies considerably and there are even occasional Type Ib/c supernovae orders of magnitude more and less luminous than the norm. The most luminous Type Ic supernovae are referred to as [[hypernova]]e and tend to have broadened light curves in addition to the increased peak luminosity. The source of the extra energy is thought to be relativistic jets driven by the formation of a rotating black hole, which also produce gamma-ray bursts.<ref>
{{cite journal
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{{cite journal
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The light curves for Type II supernovae are characterised by a much slower decline than Type I, on the order of 0.05 magnitudes per day,<ref name="barbon1979">{{cite journal
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}}</ref> excluding the plateau phase. The visual light output is dominated by kinetic energy rather than radioactive decay for several months, due primarily to the existence of hydrogen in the ejecta from the atmosphere of the supergiant progenitor star. In the initial destruction this hydrogen becomes heated and ionised. The majority of Type II supernovae show a prolonged plateau in their light curves as this hydrogen recombines, emitting visible light and becoming more transparent. This is then followed by a declining light curve driven by radioactive decay although slower than in Type I supernovae, due to the efficiency of conversion into light by all the hydrogen.<ref name="doggett"/>

In Type II-L the plateau is absent because the progenitor had relatively little hydrogen left in its atmosphere, sufficient to appear in the spectrum but insufficient to produce a noticeable plateau in the light output. In Type IIb supernovae the hydrogen atmosphere of the progenitor is so depleted (thought to be due to tidal stripping by a companion star) that the light curve is closer to a Type I supernova and the hydrogen even disappears from the spectrum after several weeks.<ref name="doggett"/>

Type IIn supernovae are characterised by additional narrow spectral lines produced in a dense shell of circumstellar material. Their light curves are generally very broad and extended, occasionally also extremely luminous and referred to as a superluminous supernova. These light curves are produced by the highly efficient conversion of kinetic energy of the ejecta into electromagnetic radiation by interaction with the dense shell of material. This only occurs when the material is sufficiently dense and compact, indicating that it has been produced by the progenitor star itself only shortly before the supernova occurs.<ref name=fillipenko1997>{{cite journal |bibcode=1997ARA&A..35..309F
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|year=1997
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Large numbers of supernovae have been catalogued and classified to provide [[Standard candle|distance candles]] and test models.<ref>{{Cite journal |last1=Hauret |first1=C |last2=Magain |first2=P |last3=Biernaux |first3=J |date=21 September 2018 |title=A cosmology-independent calibration of Type Ia supernovae data |doi-access=free |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=479 |issue=3 |pages=3996–4003 |doi=10.1093/mnras/sty1715 |arxiv=1806.10900 |bibcode=2018MNRAS.479.3996H |issn=0035-8711}}</ref><ref>{{Cite journal |last1=de Jaeger |first1=T. |last2=Galbany |first2=L. |last3=González-Gaitán |first3=S. |last4=Kessler |first4=R. |last5=Filippenko |first5=A. V. |last6=Förster |first6=F. |last7=Hamuy |first7=M. |last8=Brown |first8=P. J. |last9=Davis |first9=T. M. |last10=Gutiérrez |first10=C. P. |last11=Inserra |first11=C. |last12=Lewis |first12=G. F. |last13=Möller |first13=A. |last14=Scolnic |first14=D. |last15=Smith |first15=M. |date=11 July 2020 |title=Studying Type II supernovae as cosmological standard candles using the Dark Energy Survey |doi-access=free |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=495 |issue=4 |pages=4860–4892 |doi=10.1093/mnras/staa1402 |bibcode=2018MNRAS.479.3996H |arxiv=1806.10900 |issn=0035-8711}}</ref> Average characteristics vary somewhat with distance and type of host galaxy, but can broadly be specified for each supernova type.
{|class="wikitable" style="max-width: 600px"
|+Physical properties of supernovae by type<ref name="weidong">
{{Cite journal
 |last1=Li |first1=W.
 |last2=Leaman |first2=J.
 |last3=Chornock |first3=R.
 |last4=Filippenko |first4=A. V.
 |last5=Poznanski |first5=D.
 |last6=Ganeshalingam |first6=M.
 |last7=Wang |first7=X.
 |last8=Modjaz |first8=M.
 |last9=Jha |first9=S.
 |last10=Foley |first10=R. J.
 |last11=Smith |first11=N.
 |year=2011
 |title=Nearby supernova rates from the Lick Observatory Supernova Search – II. The observed luminosity functions and fractions of supernovae in a complete sample
 |journal=Monthly Notices of the Royal Astronomical Society
 |volume=412 |issue=3 |page=1441
 |arxiv=1006.4612
 |bibcode=2011MNRAS.412.1441L
 |doi=10.1111/j.1365-2966.2011.18160.x
|doi-access=free
 |s2cid=59467555
 }}</ref><ref name="richardson">
{{Cite journal 
 |last1=Richardson |first1=D. 
 |last2=Branch |first2=D. 
 |last3=Casebeer |first3=D. 
 |last4=Millard |first4=J. 
 |last5=Thomas |first5=R. C. 
 |last6=Baron |first6=E. 
 |year=2002 
 |title=A Comparative Study of the Absolute Magnitude Distributions of Supernovae 
 |journal=The Astronomical Journal 
 |volume=123 |issue=2 |pages=745–752 
 |arxiv=astro-ph/0112051 
 |bibcode=2002AJ....123..745R
 |doi=10.1086/338318
|s2cid=5697964 
 }}</ref>
!Type{{ref|a|a}} !!Average peak [[absolute magnitude]]{{ref|b|b}} !!Approximate energy ([[Foe (unit)|foe]]){{ref|c|c}} !!Days to peak luminosity !!Days from peak to 10% luminosity
|-
|Ia ||style="text-align:right"|−19 ||style="text-align:right"|1 ||style="text-align:right"|approx. 19 ||style="text-align:right"|around 60
|-
|Ib/c (faint) ||style="text-align:right"|around −15 ||style="text-align:right"|0.1 ||style="text-align:right"|15–25 ||style="text-align:right"|unknown
|-
|Ib ||style="text-align:right"|around −17 ||style="text-align:right"|1 ||style="text-align:right"|15–25 ||style="text-align:right"|40–100
|-
|Ic ||style="text-align:right"|around −16 ||style="text-align:right"|1 ||style="text-align:right"|15–25 ||style="text-align:right"|40–100
|-
|Ic (bright) ||style="text-align:right"|to −22 ||style="text-align:right"|above 5 ||style="text-align:right"|roughly 25 ||style="text-align:right"|roughly 100
|-
|II-b ||style="text-align:right"|around −17 ||style="text-align:right"|1 ||style="text-align:right"|around 20 ||style="text-align:right"|around 100
|-
|II-L ||style="text-align:right"|around −17 ||style="text-align:right"|1 ||style="text-align:right"|around 13 ||style="text-align:right"|around 150
|-
|II-P (faint) ||style="text-align:right"|around −14 ||style="text-align:right"|0.1 ||style="text-align:right"|roughly 15 ||style="text-align:right"|unknown
|-
|II-P ||style="text-align:right"|around −16 ||style="text-align:right"|1 ||style="text-align:right"|around 15 ||style="text-align:right"|Plateau then around 50
|-
|IIn{{ref|d|d}} ||style="text-align:right"|around −17 ||style="text-align:right"|1 ||style="text-align:right"|12–30 or more ||style="text-align:right"|50–150
|-
|IIn (bright) ||style="text-align:right"|to −22 ||style="text-align:right"|above 5 ||style="text-align:right"|above 50 ||style="text-align:right"|above 100
|}
Notes:
{{ordered list | list-style-type = lower-alpha |
| {{note|a}}Faint types may be a distinct sub-class. Bright types may be a continuum from slightly over-luminous to hypernovae.
| {{note|b}}These magnitudes are measured in the R band. Measurements in V or B bands are common and will be around half a magnitude brighter for supernovae.
| {{note|c}}[[Order of magnitude]] kinetic energy. Total electromagnetic radiated energy is usually lower, (theoretical) neutrino energy much higher.
| {{note|d}}Probably a heterogeneous group, any of the other types embedded in nebulosity.
}}

===Asymmetry===
[[Image:Chandra-crab.jpg|thumb|The [[pulsar]] in the [[Crab Nebula]] is travelling at 375 km/s relative to the nebula.<ref>
{{Cite journal
 |last1=Frail |first1=D. A.
 |last2=Giacani |first2=E. B.
 |last3=Goss |first3=W. Miller
 |last4=Dubner |first4=G. M.
 |date=1996
 |title=The Pulsar Wind Nebula Around PSR B1853+01 in the Supernova Remnant W44
 |journal=[[Astrophysical Journal Letters]]
 |volume=464 |issue=2 |pages=L165–L168
 |arxiv=astro-ph/9604121
 |bibcode=1996ApJ...464L.165F
 |doi=10.1086/310103
|s2cid=119392207
 }}</ref>]]
A long-standing puzzle surrounding Type II supernovae is why the remaining compact object receives a large velocity away from the epicentre;<ref name="Höflich-2004">
{{Cite book |first=Dong |last=Lai |editor-last1=Höflich |editor-first1=P. A. |title=NUCLEOSYNTHESIS IN TWO-DIMENSIONAL DELAYED DETONATION MODELS OF TYPE Ia SUPERNOVA EXPLOSIONS |editor-last2=Kumar |editor-first2=P. |editor-last3=Wheeler |editor-first3=J. Craig |date=2004 |publisher=[[Cambridge University Press]] |isbn=0-521-84286-7 |page=276 |chapter=Neutron star kicks and supernova asymmetry |journal=The Astrophysical Journal |volume=712 |doi=10.1088/0004-637X/712/1/624 |bibcode=2004cetd.conf..276L |arxiv=astro-ph/0312542}}</ref> [[pulsar]]s, and thus neutron stars, are observed to have high [[Peculiar velocity|peculiar velocities]], and black holes presumably do as well, although they are far harder to observe in isolation. The initial impetus can be substantial, propelling an object of more than a solar mass at a velocity of 500&nbsp;km/s or greater. This indicates an expansion asymmetry, but the mechanism by which momentum is transferred to the compact object {{As of|2023|alt=remains}} a puzzle. Proposed explanations for this kick include convection in the collapsing star, asymmetric ejection of matter during [[neutron star formation]], and asymmetrical [[neutrino]] emissions.<ref name="Höflich-2004"/><ref name="Janka-2022">{{Cite journal |last1=Janka |first1=Hans-Thomas |last2=Wongwathanarat |first2=Annop |last3=Kramer |first3=Michael |date=1 February 2022 |title=Supernova Fallback as Origin of Neutron Star Spins and Spin-kick Alignment |doi-access=free |journal=The Astrophysical Journal |volume=926 |issue=1 |page=9 |doi=10.3847/1538-4357/ac403c |bibcode=2022ApJ...926....9J |arxiv=2104.07493 |issn=0004-637X}}</ref>

One possible explanation for this asymmetry is large-scale [[convection]] above the core. The convection can create radial variations in density giving rise to variations in the amount of energy absorbed from neutrino outflow.<ref name="Janka-2007"/> However analysis of this mechanism predicts only modest momentum transfer.<ref name=Fryer-2004>
{{Cite journal
 |last=Fryer |first=C. L.
 |date=2004
 |title=Neutron Star Kicks from Asymmetric Collapse
 |journal=[[Astrophysical Journal]]
 |volume=601 |issue=2 |pages=L175–L178
 |arxiv=astro-ph/0312265
 |bibcode=2004ApJ...601L.175F
 |doi=10.1086/382044
|s2cid=1473584
 }}</ref> Another possible explanation is that accretion of gas onto the central neutron star can create a [[accretion disk|disk]] that drives highly directional jets, propelling matter at a high velocity out of the star, and driving transverse shocks that completely disrupt the star. These jets might play a crucial role in the resulting supernova.<ref>
{{cite journal
 |last1=Gilkis |first1=A.
 |last2=Soker |first2=N.
 |year=2014
 |title=Implications of turbulence for jets in core-collapse supernova explosions
 |journal=The Astrophysical Journal
 |volume=806 |issue=1 |page=28
 |arxiv=1412.4984
 |doi=10.1088/0004-637X/806/1/28
 |bibcode=2015ApJ...806...28G
|s2cid=119002386
 }}</ref><ref>
{{cite journal
 |last1=Khokhlov |first1=A. M.
 |last2=Höflich |first2=P. A.
 |last3=Oran |first3=E. S.
 |last4=Wheeler |first4=J. Craig
 |last5=Wang |first5=L.
 |last6=Chtchelkanova |first6=A. Yu.
 |year=1999
 |title=Jet-induced Explosions of Core Collapse Supernovae
 |journal=The Astrophysical Journal
 |volume=524 |issue=2 |pages=L107
 |arxiv=astro-ph/9904419
 |bibcode=1999ApJ...524L.107K
 |doi=10.1086/312305
|s2cid=37572204
 }}</ref> (A similar model is used for explaining long gamma-ray bursts.) The dominant mechanism may depend upon the mass of the progenitor star.<ref name="Janka-2022"/>

Initial asymmetries have also been confirmed in Type Ia supernovae through observation. This result may mean that the initial luminosity of this type of supernova depends on the viewing angle. However, the expansion becomes more symmetrical with the passage of time. Early asymmetries are detectable by measuring the polarisation of the emitted light.<ref>
{{cite journal
 |last1=Wang |first1=L.
 |last2=Baade |first2=D.
 |last3=Höflich |first3=P. A.
 |last4=Khokhlov |first4=A. M.
 |last5=Wheeler |first5=J. C.
 |last6=Kasen |first6=D.
 |last7=Nugent |first7=P. E.
 |last8=Perlmutter |first8=S. A.
 |last9=Fransson |first9=C.
 |last10=Lundqvist |first10=P.
 |year=2003
 |title=Spectropolarimetry of SN 2001el in NGC 1448: Asphericity of a Normal Type Ia Supernova
 |journal=The Astrophysical Journal
 |volume=591 |issue=2 |pages=1110–1128
 |arxiv=astro-ph/0303397
 |bibcode=2003ApJ...591.1110W 
 |doi=10.1086/375444
|s2cid=2923640
 }}</ref>

===Energy output===
[[Image:SNIacurva.png|thumb|The radioactive decays of nickel-56 and cobalt-56 that produce a supernova visible light curve<ref name="explosion_model"/><ref name="mazzali"/>]]
Although supernovae are primarily known as luminous events, the [[electromagnetic radiation]] they release is almost a minor side-effect. Particularly in the case of core collapse supernovae, the emitted electromagnetic radiation is a tiny fraction of the total energy released during the event.<ref>{{cite journal |doi=10.1126/science.1075935 |title=The Secrets Behind Supernovae |year=2002 |last1=Janka |first1=H.-Th. |journal=Science |volume=297 |issue=5584 |pages=1134–1135 |pmid=12183617 |s2cid=34349443 }}</ref>

There is a fundamental difference between the balance of energy production in the different types of supernova. In Type Ia white dwarf detonations, most of the energy is directed into [[nucleosynthesis|heavy element synthesis]] and the [[kinetic energy]] of the ejecta.<ref>{{cite journal |doi=10.1126/science.276.5317.1378|title=Type Ia Supernovae: Their Origin and Possible Applications in Cosmology |year=1997 |last1=Nomoto |first1=Ken'Ichi |last2=Iwamoto |first2=Koichi |last3=Kishimoto |first3=Nobuhiro |journal=Science |volume=276 |issue=5317 |pages=1378–1382 |pmid=9190677 |arxiv=astro-ph/9706007 |bibcode=1997Sci...276.1378N |s2cid=2502919 }}</ref> In core collapse supernovae, the vast majority of the energy is directed into [[supernova neutrino|neutrino]] emission, and while some of this apparently powers the observed destruction, 99%+ of the neutrinos escape the star in the first few minutes following the start of the collapse.<ref name="Antonioli-2004"/>

Standard Type Ia supernovae derive their energy from a runaway nuclear fusion of a carbon-oxygen white dwarf. The details of the energetics are still not fully understood, but the result is the ejection of the entire mass of the original star at high kinetic energy. Around half a solar mass of that mass is [[nickel-56|<sup>56</sup>Ni]] generated from [[Silicon-burning process|silicon burning]]. <sup>56</sup>Ni is [[radioactive]] and decays into [[cobalt-56|<sup>56</sup>Co]] by [[beta plus decay]] (with a [[half life]] of six days) and gamma rays. <sup>56</sup>Co itself decays by the beta plus ([[positron]]) path with a half-life of 77 days into stable <sup>56</sup>Fe. These two processes are responsible for the electromagnetic radiation from Type Ia supernovae. In combination with the changing transparency of the ejected material, they produce the rapidly declining light curve.<ref name="mazzali"/>

Core collapse supernovae are on average visually fainter than Type Ia supernovae,<ref name="Springer-2016"/><ref name="Modjaz-2019"/><ref name="Nyholm-2020"/> but the total energy released is far higher, as outlined in the following table.

{|class="wikitable"
|+Energetics of supernovae
!Supernova !!Approximate total energy<br/>x10<sup>44</sup> joules ([[Foe (unit)|foe]]){{ref|c|c}} !!Ejected Ni<br/>(solar masses) !!Neutrino energy<br/>(foe) !!Kinetic energy<br/>(foe) !!Electromagnetic radiation<br/>(foe)
|-
|Type Ia<ref name="mazzali">{{Cite journal
 |last1=Mazzali
 |first1=P. A.
 |last2=Nomoto
 |first2=K. I.
 |last3=Cappellaro
 |first3=E.
 |last4=Nakamura
 |first4=T.
 |last5=Umeda
 |first5=H.
 |last6=Iwamoto
 |first6=K.
 |year=2001
 |title=Can Differences in the Nickel Abundance in Chandrasekhar-Mass Models Explain the Relation between the Brightness and Decline Rate of Normal Type Ia Supernovae?
 |journal=The Astrophysical Journal
 |volume=547
 |issue=2
 |page=988
 |arxiv=astro-ph/0009490
 |bibcode=2001ApJ...547..988M
 |doi=10.1086/318428 |doi-access=free
 |s2cid=9324294
 }}</ref><ref>
{{Cite journal
 |last1=Iwamoto |first1=K.
 |year=2006
 |title=Neutrino Emission from Type Ia Supernovae
 |journal=AIP Conference Proceedings
 |volume=847 |pages=406–408
 |doi=10.1063/1.2234440
|bibcode=2006AIPC..847..406I
 }}</ref><ref>
{{Cite journal
 |last1=Hayden |first1=B. T.
 |last2=Garnavich |first2=P. M.
 |last3=Kessler |first3=R.
 |last4=Frieman |first4=J. A.
 |last5=Jha |first5=S. W.
 |last6=Bassett |first6=B.
 |last7=Cinabro |first7=D.
 |last8=Dilday |first8=B.
 |last9=Kasen |first9=D.
 |last10=Marriner |first10=J.
 |last11=Nichol |first11=R. C.
 |last12=Riess |first12=A. G.
 |last13=Sako |first13=M.
 |last14=Schneider |first14=D. P.
 |last15=Smith |first15=M.
 |last16=Sollerman |first16=J.
 |year=2010
 |title=The Rise and Fall of Type Ia Supernova Light Curves in the SDSS-II Supernova Survey
 |journal=The Astrophysical Journal
 |volume=712 |issue=1 |pages=350–366
 |arxiv=1001.3428
 |bibcode=2010ApJ...712..350H
 |doi=10.1088/0004-637X/712/1/350
|s2cid=118463541
 }}</ref> ||style="text-align:right"|1.5 ||style="text-align:right"|0.4 – 0.8 ||style="text-align:right"|0.1 ||style="text-align:right"|1.3 – 1.4 ||style="text-align:right"|~0.01
|-
|Core collapse<ref>
{{cite journal
 |last1=Janka |first1=H.-T.
 |year=2012
 |title=Explosion Mechanisms of Core-Collapse Supernovae
 |journal=[[Annual Review of Nuclear and Particle Science]]
 |volume=62 |issue=1 |pages=407–451
 |arxiv=1206.2503
 |bibcode=2012ARNPS..62..407J
 |doi=10.1146/annurev-nucl-102711-094901|doi-access=free
|s2cid=118417333
 }}</ref><ref>
{{cite journal
 |last1=Smartt |first1=Stephen J.
 |last2=Nomoto |first2=Ken'ichi
 |last3=Cappellaro |first3=Enrico
 |last4=Nakamura |first4=Takayoshi
 |last5=Umeda |first5=Hideyuki
 |last6=Iwamoto |first6=Koichi
 |date=2009
 |title=Progenitors of core-collapse supernovae
 |journal=[[Annual Review of Astronomy and Astrophysics]]
 |volume=47 |issue=1 |pages=63–106
 |arxiv=0908.0700
 |bibcode=2009ARA&A..47...63S
 |doi=10.1146/annurev-astro-082708-101737
|s2cid=55900386
 }}</ref> ||style="text-align:right"|100 ||style="text-align:right"|(0.01) – 1 ||style="text-align:right"|100 ||style="text-align:right"|1 ||style="text-align:right"|0.001 – 0.01
|-
|Hypernova ||style="text-align:right"|100 ||style="text-align:right"|~1 ||style="text-align:right"|1–100 ||style="text-align:right"|1–100 ||style="text-align:right"|~0.1
|-
|Pair instability<ref name=kasen/> ||style="text-align:right"|5–100 ||style="text-align:right"|0.5 – 50 ||style="text-align:right"|low? ||style="text-align:right"|1–100 ||style="text-align:right"|0.01 – 0.1
|}

In some core collapse supernovae, fallback onto a black hole drives [[relativistic jet]]s which may produce a brief energetic and directional burst of gamma rays and also transfers substantial further energy into the ejected material. This is one scenario for producing high-luminosity supernovae and is thought to be the cause of Type Ic hypernovae and long-duration gamma-ray bursts.<ref>{{Cite journal |last1=Dessart |first1=L. |last2=Burrows |first2=A. |last3=Livne |first3=E. |last4=Ott |first4=C. D. |date=20 January 2008 |title=The Proto-Neutron Star Phase of the Collapsar Model and the Route to Long-Soft Gamma-Ray Bursts and Hypernovae |doi-access=free |journal=The Astrophysical Journal |language=en |volume=673 |issue=1 |pages=L43–L46 |bibcode=2008ApJ...673L..43D |arxiv=0710.5789 |doi=10.1086/527519 |issn=0004-637X}}</ref> If the relativistic jets are too brief and fail to penetrate the stellar envelope then a low-luminosity gamma-ray burst may be produced and the supernova may be sub-luminous.<ref>{{Cite journal |last1=Senno |first1=Nicholas |last2=Murase |first2=Kohta |last3=Mészáros |first3=Peter |date=8 April 2016 |title=Choked jets and low-luminosity gamma-ray bursts as hidden neutrino sources |url=https://link.aps.org/doi/10.1103/PhysRevD.93.083003 |journal=Physical Review D |language=en |volume=93 |issue=8 |article-number=083003 |doi=10.1103/PhysRevD.93.083003 |bibcode=2016PhRvD..93h3003S |arxiv=1512.08513 |s2cid=16452722 |issn=2470-0010}}</ref>

When a supernova occurs inside a small dense cloud of circumstellar material, it will produce a shock wave that can efficiently convert a high fraction of the kinetic energy into electromagnetic radiation. Even though the initial energy was entirely normal the resulting supernova will have high luminosity and extended duration since it does not rely on exponential radioactive decay. This type of event may cause Type IIn hypernovae.<ref>{{Cite journal |last1=Woosley |first1=S. E. |last2=Blinnikov |first2=S. |last3=Heger |first3=Alexander |date=15 November 2007 |title=Pulsational pair instability as an explanation for the most luminous supernovae |url=https://www.nature.com/articles/nature06333 |journal=Nature |language=en |volume=450 |issue=7168 |pages=390–392 |bibcode=2007Natur.450..390W |arxiv=0710.3314 |doi=10.1038/nature06333 |pmid=18004378 |s2cid=2925738 |issn=0028-0836}}</ref><ref>{{Cite journal |last1=Barkov |first1=Maxim V. |last2=Komissarov |first2=Serguei S. |date=21 July 2011 |title=Recycling of neutron stars in common envelopes and hypernova explosions: Recycling of neutron stars and hypernovae |doi-access=free |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=415 |issue=1 |pages=944–958 |doi=10.1111/j.1365-2966.2011.18762.x |bibcode=2011MNRAS.415..944B |arxiv=1012.4565 }}</ref>

Although pair-instability supernovae are core collapse supernovae with spectra and light curves similar to Type II-P, the nature after core collapse is more like that of a giant Type Ia with runaway fusion of carbon, oxygen and silicon. The total energy released by the highest-mass events is comparable to other core collapse supernovae but neutrino production is thought to be very low, hence the kinetic and electromagnetic energy released is very high. The cores of these stars are much larger than any white dwarf and the amount of radioactive nickel and other heavy elements ejected from their cores can be orders of magnitude higher, with consequently high visual luminosity.<ref>{{Cite journal |last1=Wright |first1=Warren P. |last2=Gilmer |first2=Matthew S. |last3=Fröhlich |first3=Carla |last4=Kneller |first4=James P. |date=13 November 2017 |title=Neutrino signal from pair-instability supernovae |url=https://link.aps.org/doi/10.1103/PhysRevD.96.103008 |journal=Physical Review D |language=en |volume=96 |issue=10 |article-number=103008 |bibcode=2017PhRvD..96j3008W |arxiv=1706.08410 |doi=10.1103/PhysRevD.96.103008 |s2cid=119487775 |issn=2470-0010}}</ref>

===Progenitor===
[[File:Artist's impression time-lapse of distant supernovae.webm|thumb|Occasional supernovae appear in this sped-up artist's impression of distant galaxies. Each exploding star briefly rivals the brightness of its host galaxy.]]
The supernova classification type is closely tied to the type of progenitor star at the time of the collapse. The occurrence of each type of supernova depends on the star's metallicity, since this affects the strength of the stellar wind and thereby the rate at which the star loses mass.<ref>{{Cite journal |last1=Ganss |first1=R |last2=Pledger |first2=J L |last3=Sansom |first3=A E |last4=James |first4=P A |last5=Puls |first5=J |last6=Habergham-Mawson |first6=S M |date=22 March 2022 |title=Metallicity estimation of core-collapse Supernova H ii regions in galaxies within 30 Mpc |doi-access=free|journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=512 |issue=1 |pages=1541–1556 |doi=10.1093/mnras/stac625 |issn=0035-8711 |bibcode=2022MNRAS.512.1541G |arxiv=2203.03308 }}</ref>

Type Ia supernovae are produced from white dwarf stars in binary star systems and occur in all [[Galaxy morphological classification|galaxy types]].<ref>{{Cite journal |last1=Prochaska |first1=J. X. |last2=Bloom |first2=J. S. |last3=Chen |first3=H.-W. |last4=Foley |first4=R. J. |last5=Perley |first5=D. A. |last6=Ramirez-Ruiz |first6=E. |last7=Granot |first7=J. |last8=Lee |first8=W. H. |last9=Pooley |first9=D. |last10=Alatalo |first10=K. |last11=Hurley |first11=K. |last12=Cooper |first12=M. C. |last13=Dupree |first13=A. K. |last14=Gerke |first14=B. F. |last15=Hansen |first15=B. M. S. |date=10 May 2006 |title=The Galaxy Hosts and Large-Scale Environments of Short-Hard Gamma-Ray Bursts |doi-access=free |journal=The Astrophysical Journal |language=en |volume=642 |issue=2 |pages=989–994 |doi=10.1086/501160 |issn=0004-637X |bibcode=2006ApJ...642..989P |arxiv=astro-ph/0510022 }}</ref> Core collapse supernovae are only found in galaxies undergoing current or very recent star formation, since they result from short-lived massive stars. They are most commonly found in type Sc spirals, but also in the arms of other spiral galaxies and in [[irregular galaxy|irregular galaxies]], especially [[Starburst galaxy|starburst galaxies]].<ref>{{Cite journal |last1=Petrosian |first1=Artashes |last2=Navasardyan |first2=Hripsime |last3=Cappellaro |first3=Enrico |last4=McLean |first4=Brian |last5=Allen |first5=Ron |last6=Panagia |first6=Nino |last7=Leitherer |first7=Claus |last8=MacKenty |first8=John |last9=Turatto |first9=Massimo |date=March 2005 |title=Active and Star-forming Galaxies and Their Supernovae |doi-access=free |journal=The Astronomical Journal |language=en |volume=129 |issue=3 |pages=1369–1380 |doi=10.1086/427712 |bibcode=2005AJ....129.1369P |issn=0004-6256}}</ref><ref>{{Cite journal |last1=Shao |first1=X. |last2=Liang |first2=Y. C. |last3=Dennefeld |first3=M. |last4=Chen |first4=X. Y. |last5=Zhong |first5=G. H. |last6=Hammer |first6=F. |last7=Deng |first7=L. C. |last8=Flores |first8=H. |last9=Zhang |first9=B. |last10=Shi |first10=W. B. |last11=Zhou |first11=L. |date=25 July 2014 |title=Comparing the Host Galaxies of Type Ia, Type II, and Type Ibc Supernovae |doi-access=free |journal=The Astrophysical Journal |volume=791 |issue=1 |page=57 |doi=10.1088/0004-637X/791/1/57 |bibcode=2014ApJ...791...57S |arxiv=1407.0483 |issn=0004-637X}}</ref><ref>{{Cite journal |last1=Taggart |first1=K |last2=Perley |first2=D A |date=5 April 2021 |title=Core-collapse, superluminous, and gamma-ray burst supernova host galaxy populations at low redshift: the importance of dwarf and starbursting galaxies |doi-access=free |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=503 |issue=3 |pages=3931–3952 |bibcode=2021MNRAS.503.3931T |arxiv=1911.09112 |doi=10.1093/mnras/stab174 |issn=0035-8711}}</ref>

Type Ib and Ic supernovae are hypothesised to have been produced by core collapse of massive stars that have lost their outer layer of hydrogen and helium, either via strong stellar winds or mass transfer to a companion.<ref name="arxiv"/> They normally occur in regions of new star formation, and are extremely rare in [[Elliptical galaxy|elliptical galaxies]].<ref name="Perets-2010"/> The progenitors of Type IIn supernovae also have high rates of mass loss in the period just prior to their explosions.<ref>{{Cite journal |last1=Moriya |first1=Takashi J. |last2=Maeda |first2=Keiichi |last3=Taddia |first3=Francesco |last4=Sollerman |first4=Jesper |last5=Blinnikov |first5=Sergei I. |last6=Sorokina |first6=Elena I. |date=11 April 2014 |title=Mass-loss histories of Type IIn supernova progenitors within decades before their explosion |doi-access=free |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=439 |issue=3 |pages=2917–2926 |bibcode=2014MNRAS.439.2917M |arxiv=1401.4893 |doi=10.1093/mnras/stu163 |issn=1365-2966}}</ref> Type Ic supernovae have been observed to occur in regions that are more metal-rich and have higher star-formation rates than average for their host galaxies.<ref>{{Cite journal |last1=Galbany |first1=L. |last2=Anderson |first2=J. P. |last3=Sánchez |first3=S. F. |last4=Kuncarayakti |first4=H. |last5=Pedraz |first5=S. |last6=González-Gaitán |first6=S. |last7=Stanishev |first7=V. |last8=Domínguez |first8=I. |last9=Moreno-Raya |first9=M. E. |last10=Wood-Vasey |first10=W. M. |last11=Mourão |first11=A. M. |last12=Ponder |first12=K. A. |last13=Badenes |first13=C. |last14=Mollá |first14=M. |last15=López-Sánchez |first15=A. R. |date=13 March 2018 |title=PISCO: The PMAS/PPak Integral-field Supernova Hosts Compilation |doi-access=free |journal=The Astrophysical Journal |volume=855 |issue=2 |page=107 |doi=10.3847/1538-4357/aaaf20 |bibcode=2018ApJ...855..107G |arxiv=1802.01589 |issn=1538-4357}}</ref> The table shows the progenitor for the main types of core collapse supernova, and the approximate proportions that have been observed in the local neighbourhood.
{|class="wikitable"
|+ Fraction of core collapse supernovae types by progenitor<ref name=eldridge/>
|-
! Type !! Progenitor star !! Fraction
|-
|Ib ||WC [[Wolf–Rayet star|Wolf–Rayet]] or [[helium star]] ||9.0%
|-
|Ic ||WO [[Wolf–Rayet star|Wolf–Rayet]] ||17.0%
|-
|II-P ||[[Supergiant]] ||55.5%
|-
|II-L ||[[Supergiant]] with a depleted hydrogen shell ||3.0%
|-
|IIn ||[[Supergiant]] in a dense cloud of expelled material (such as [[Luminous blue variable|LBV]])||2.4%
|-
|IIb ||[[Supergiant]] with highly depleted hydrogen (stripped by companion?) ||12.1%
|-
|IIpec ||[[Blue supergiant]]||1.0%
|}

[[File:Supernovae as initial mass-metallicity.svg|upright=1.8|thumb|Supernova types by initial mass-metallicity]]
[[File:Remnants of single massive stars.svg|upright=1.8|thumb|Remnants of single massive stars]]

There are a number of difficulties reconciling modelled and observed stellar evolution leading up to core collapse supernovae. Red supergiants are the progenitors for the vast majority of core collapse supernovae, and these have been observed but only at relatively low masses and luminosities, below about {{solar mass|18}} and {{solar luminosity|100,000}}, respectively. Most progenitors of Type II supernovae are not detected and must be considerably fainter, and presumably less massive. This discrepancy has been referred to as the '''red supergiant problem'''.<ref name="davies2020"/> It was first described in 2009 by Stephen Smartt, who also coined the term. After performing a volume-limited search for supernovae, Smartt et al. found the lower and upper mass limits for Type II-P supernovae to form to be {{solar mass|{{val|8.5|1|1.5}}}} and {{solar mass|{{val|16.5|1.5}}}}, respectively. The former is consistent with the expected upper mass limits for white dwarf progenitors to form, but the latter is not consistent with massive star populations in the Local Group.<ref name=smartt2009>{{Cite journal |last1=Smartt |first1=S. J. |last2=Eldridge |first2=J. J. |last3=Crockett |first3=R. M. |last4=Maund |first4=J. R. |date=May 2009 |title=The death of massive stars – I. Observational constraints on the progenitors of Type II-P supernovae |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=395 |issue=3 |pages=1409–1437 |arxiv=0809.0403 |bibcode=2009MNRAS.395.1409S |doi=10.1111/j.1365-2966.2009.14506.x |doi-access=free |s2cid=3228766 |issn=0035-8711}}</ref> The upper limit for red supergiants that produce a visible supernova explosion has been calculated at {{val|19|4|2|u=solar mass}}.<ref name=davies2020>{{cite journal |bibcode=2020MNRAS.496L.142D |arxiv=2005.13855 |doi=10.1093/mnrasl/slaa102 |title='On the red supergiant problem': A rebuttal, and a consensus on the upper mass cut-off for II-P progenitors |year=2020 |last1=Davies |first1=Ben |last2=Beasor |first2=Emma R. |journal=Monthly Notices of the Royal Astronomical Society: Letters |volume=496 |issue=1 |pages=L142–L146 |doi-access=free }}</ref>

It is thought that higher mass red supergiants do not explode as supernovae, but instead evolve back towards hotter temperatures. Several progenitors of Type IIb supernovae have been confirmed, and these were K and G supergiants, plus one A supergiant.<ref name=smartt/> Yellow hypergiants or LBVs are proposed progenitors for Type IIb supernovae, and almost all Type IIb supernovae near enough to observe have shown such progenitors.<ref name=problem>
{{Cite journal
 |last1=Walmswell |first1=J. J.
 |last2=Eldridge |first2=J. J.
 |doi=10.1111/j.1365-2966.2011.19860.x
 |title=Circumstellar dust as a solution to the red supergiant supernova progenitor problem
 |journal=Monthly Notices of the Royal Astronomical Society
 |volume=419 |issue=3 |page=2054
 |year=2012
|doi-access=free
 |arxiv=1109.4637
 |bibcode=2012MNRAS.419.2054W
|s2cid=118445879
 }}</ref><ref name=ysg>
{{Cite journal
 |last1=Georgy |first1=C.
 |doi=10.1051/0004-6361/201118372
 |title=Yellow supergiants as supernova progenitors: An indication of strong mass loss for red supergiants?
 |journal=Astronomy & Astrophysics
 |volume=538 |pages=L8–L2 |year=2012
|arxiv=1111.7003 |bibcode=2012A&A...538L...8G
|s2cid=55001976
 }}</ref>
[[File:Stellar evolution v2024.png|alt=Infographic showing arrows between circles representing stellar evolution and how it varies by mass|thumb|Approximate stellar evolution pathways of supernova progenitor stars (and lower mass stars) with circle size reflecting relative size and color related to temperature]]
Blue supergiants form an unexpectedly high proportion of confirmed supernova progenitors, partly due to their high luminosity and easy detection, while not a single Wolf–Rayet progenitor has yet been clearly identified.<ref name=smartt>
{{cite journal
|bibcode=2009ARA&A..47...63S
|title=Progenitors of Core-Collapse Supernovae
|journal=[[Annual Review of Astronomy & Astrophysics]]
|volume=47 |issue=1 |pages=63–106
|year=2009 |doi=10.1146/annurev-astro-082708-101737
|arxiv=0908.0700
|last1=Smartt
|first1=Stephen J.
|last2=Thompson
|first2=Todd A.
|last3=Kochanek
|first3=Christopher S.
|s2cid=55900386
}}</ref><ref name=yoon/> Models have had difficulty showing how blue supergiants lose enough mass to reach supernova without progressing to a different evolutionary stage. One study has shown a possible route for low-luminosity post-red supergiant luminous blue variables to collapse, most likely as a Type IIn supernova.<ref name=lbv>
{{Cite journal
 |last1=Groh |first1=J. H.
 |last2=Meynet |first2=G.
 |last3=Ekström |first3=S.
 |title=Massive star evolution: Luminous blue variables as unexpected supernova progenitors
 |doi=10.1051/0004-6361/201220741
 |journal=Astronomy & Astrophysics
 |volume=550 |pages=L7 |year=2013
|arxiv=1301.1519
 |bibcode=2013A&A...550L...7G
|s2cid=119227339
 }}</ref> Several examples of hot luminous progenitors of Type IIn supernovae have been detected: [[SN 2005gy]] and [[SN 2010jl]] were both apparently massive luminous stars, but are very distant; and [[SN 2009ip]] had a highly luminous progenitor likely to have been an LBV, but is a peculiar supernova whose exact nature is disputed.<ref name=smartt/>

The progenitors of Type Ib/c supernovae are not observed at all, and constraints on their possible luminosity are often lower than those of known [[WC star]]s.<ref name=smartt/> [[WO star]]s are extremely rare and visually relatively faint, so it is difficult to say whether such progenitors are missing or just yet to be observed. Very luminous progenitors have not been securely identified, despite numerous supernovae being observed near enough that such progenitors would have been clearly imaged.<ref name=yoon>
{{cite journal
|bibcode=2012A&A...544L..11Y
|title=On the nature and detectability of Type Ib/c supernova progenitors
|journal=Astronomy & Astrophysics
|volume=544|pages=L11
|year=2012
|doi=10.1051/0004-6361/201219790
|arxiv=1207.3683|last1=Yoon
|first1=S.-C.
|last2=Gräfener
|first2=G.
|last3=Vink
|first3=J. S.
|last4=Kozyreva
|first4=A.
|last5=Izzard
|first5=R. G.
|s2cid=118596795
}}</ref> Population modelling shows that the observed Type Ib/c supernovae could be reproduced by a mixture of single massive stars and stripped-envelope stars from interacting binary systems.<ref name=eldridge/> The continued lack of unambiguous detection of progenitors for normal Type Ib and Ic supernovae may be due to most massive stars collapsing directly to a black hole [[failed supernova|without a supernova outburst]]. Most of these supernovae are then produced from lower-mass low-luminosity helium stars in binary systems. A small number would be from rapidly rotating massive stars, likely corresponding to the highly energetic Type Ic-BL events that are associated with long-duration gamma-ray bursts.<ref name=smartt/>

==External impact==
Supernovae events generate heavier elements that are scattered throughout the surrounding interstellar medium. The expanding shock wave from a supernova can trigger star formation. Galactic cosmic rays are generated by supernova explosions.

===Source of heavy elements===
{{Main|Stellar nucleosynthesis|Supernova nucleosynthesis}}
[[File:Nucleosynthesis periodic table.svg|thumb|upright=2|Periodic table showing the source of each element in the interstellar medium]]

Supernovae are a major source of elements in the interstellar medium from oxygen through to rubidium,<ref name=nucleosynthesis/><ref name="François">
{{Cite journal
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 |last2=Matteucci |first2=F.
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 |last4=Spite |first4=M.
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 |date=2004
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 |volume=421 |issue=2 |pages=613–621
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 |bibcode=2004A&A...421..613F
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{{cite book
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 |year=1977
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}}</ref> though the theoretical abundances of the elements produced or seen in the spectra varies significantly depending on the various supernova types.<ref name="Truran"/> Type Ia supernovae produce mainly silicon and iron-peak elements, metals such as nickel and iron.<ref name=nomoto2018>{{cite journal|doi=10.1007/s11214-018-0499-0|title=Single Degenerate Models for Type Ia Supernovae: Progenitor's Evolution and Nucleosynthesis Yields|journal=Space Science Reviews|volume=214|issue=4|year=2018|last1=Nomoto|first1=Ken'Ichi|last2=Leung|first2=Shing-Chi|page=67|arxiv=1805.10811|bibcode=2018SSRv..214...67N|s2cid=118951927}}</ref><ref name=maeda>{{cite journal|doi=10.1088/0004-637X/712/1/624|title=Nucleosynthesis in Two-Dimensional Delayed Detonation Models of Type Ia Supernova Explosions|journal=The Astrophysical Journal|volume=712|pages=624–638|year=2010|last1=Maeda|first1=K.|last2=Röpke|first2=F.K.|last3=Fink|first3=M.|last4=Hillebrandt|first4=W.|last5=Travaglio|first5=C.|last6=Thielemann|first6=F.-K.|issue=1|arxiv=1002.2153|bibcode=2010ApJ...712..624M|s2cid=119290875}}</ref> Core collapse supernovae eject much smaller quantities of the iron-peak elements than Type Ia supernovae, but larger masses of light [[alpha element]]s such as oxygen and neon, and elements heavier than zinc. The latter is especially true with electron capture supernovae.<ref>{{Cite journal|doi = 10.1088/2041-8205/726/2/L15|title = Electron-Capture Supernovae as the Origin of Elements Beyond Iron|year = 2011|last1 = Wanajo|first1 = Shinya|last2 = Janka|first2 = Hans-Thomas|last3 = Müller|first3 = Bernhard|journal = The Astrophysical Journal|volume = 726|issue = 2|pages = L15|arxiv = 1009.1000|bibcode = 2011ApJ...726L..15W|s2cid = 119221889}}</ref> The bulk of the material ejected by Type II supernovae is hydrogen and helium.<ref name=eichler>{{cite journal|doi=10.1088/1361-6471/aa8891|title=Nucleosynthesis in 2D core-collapse supernovae of 11.2 and 17.0 M⊙ progenitors: Implications for Mo and Ru production|journal=Journal of Physics G: Nuclear and Particle Physics|volume=45|page=014001|year=2018|last1=Eichler|first1=M.|last2=Nakamura|first2=K.|last3=Takiwaki|first3=T.|last4=Kuroda|first4=T.|last5=Kotake|first5=K.|last6=Hempel|first6=M.|last7=Cabezón|first7=R.|last8=Liebendörfer|first8=M.|last9=Thielemann|first9=F-K|issue=1|arxiv=1708.08393|bibcode=2018JPhG...45a4001E|s2cid=118936429}}</ref> The heavy elements are produced by: nuclear fusion for nuclei up to <sup>34</sup>S; silicon photodisintegration rearrangement and quasiequilibrium during silicon burning for nuclei between <sup>36</sup>Ar and <sup>56</sup>Ni; and rapid capture of neutrons ([[r-process]]) during the supernova's collapse for elements heavier than iron. <!--Nucleosynthesis during silicon burning yields nuclei roughly 1,000 to 100,000 times more abundant than the r-process isotopes heavier than iron.<ref>
{{Cite journal
 |last=Woosley |first=S. E.
 |last2=Arnett |first2=W. D.
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 |journal=[[Astrophysical Journal Supplement]]
 |volume=26 |pages=231–312
 |bibcode=1973ApJS...26..231W
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}}</ref>--> The r-process produces highly unstable nuclei that are rich in [[neutron]]s and that rapidly beta decay into more stable forms. In supernovae, r-process reactions are responsible for about half of all the isotopes of elements beyond iron,<ref>
{{Cite journal
 |last1=Qian |first1=Y.-Z.
 |last2=Vogel |first2=P.
 |last3=Wasserburg |first3=G. J.
 |date=1998
 |title=Diverse Supernova Sources for the r-Process
 |journal=[[Astrophysical Journal]]
 |volume=494 |issue=1 |pages=285–296
 |bibcode=1998ApJ...494..285Q
 |doi=10.1086/305198
|arxiv=astro-ph/9706120|s2cid=15967473
 }}</ref> although [[neutron star merger]]s may be the main astrophysical source for many of these elements.<ref name=nucleosynthesis>{{cite journal|doi=10.1126/science.aau9540|pmid=30705182|title=Populating the periodic table: Nucleosynthesis of the elements|journal=Science|volume=363|issue=6426|pages=474–478|year=2019|last1=Johnson|first1=Jennifer A.|bibcode=2019Sci...363..474J|s2cid=59565697|doi-access=free}}</ref><ref name=siegel>{{cite journal |doi=10.1038/s41586-019-1136-0 |pmid=31068724 |title=Collapsars as a major source of r-process elements |journal=Nature |volume=569 |issue=7755 |pages=241–244 |year=2019 |last1=Siegel |first1=Daniel M. |last2=Barnes |first2=Jennifer |last3=Metzger |first3=Brian D. |arxiv=1810.00098 |bibcode=2019Natur.569..241S |s2cid=73612090 }}</ref>

In the modern universe, old [[asymptotic giant branch]] (AGB) stars are the dominant source of dust from oxides, carbon and [[s-process]] elements.<ref name=nucleosynthesis/><ref>
{{cite journal
 |last1=Gonzalez |first1=G.
 |last2=Brownlee |first2=D.
 |last3=Ward |first3=P.
 |year=2001
 |title=The Galactic Habitable Zone: Galactic Chemical Evolution
 |journal=Icarus
 |volume=152 |issue=1 |page=185
 |arxiv=astro-ph/0103165
 |bibcode=2001Icar..152..185G
 |doi=10.1006/icar.2001.6617
|s2cid=18179704
 }}</ref> However, in the early universe, before AGB stars formed, supernovae may have been the main source of dust.<ref name=dust>{{cite journal |bibcode=2019BAAS...51c.351R |arxiv=1904.08485 |last1=Rho |first1=Jeonghee |title=Astro2020 Science White Paper: Are Supernovae the Dust Producer in the Early Universe? |journal=Bulletin of the American Astronomical Society |volume=51 |issue=3 |page=351 |last2=Milisavljevic |first2=Danny |last3=Sarangi |first3=Arkaprabha |last4=Margutti |first4=Raffaella |last5=Chornock |first5=Ryan |last6=Rest |first6=Armin |last7=Graham |first7=Melissa |last8=Craig Wheeler |first8=J. |last9=DePoy |first9=Darren |last10=Wang |first10=Lifan |last11=Marshall |first11=Jennifer |last12=Williams |first12=Grant |last13=Street |first13=Rachel |last14=Skidmore |first14=Warren |last15=Haojing |first15=Yan |last16=Bloom |first16=Joshua |last17=Starrfield|author17-link=Sumner Starrfield |first17=Sumner |last18=Lee |first18=Chien-Hsiu |last19=Cowperthwaite |first19=Philip S. |last20=Stringfellow |first20=Guy S. |last21=Coppejans |first21=Deanne |last22=Terreran |first22=Giacomo |last23=Sravan |first23=Niharika |last24=Geballe |first24=Thomas R. |last25=Evans |first25=Aneurin |last26=Marion |first26=Howie |year=2019 |doi=10.1088/2041-8205/788/1/L14 }}
</ref>

===Role in stellar evolution===
{{Main|Supernova remnant}}
Remnants of many supernovae consist of a compact object and a rapidly expanding shock wave of material. This cloud of material sweeps up surrounding [[interstellar medium]] during a free expansion phase, which can last for up to two centuries. The wave then gradually undergoes a period of [[adiabatic process|adiabatic expansion]], and will slowly cool and mix with the surrounding interstellar medium over a period of about 10,000 years.<ref>
{{cite journal
 |last1=Cox |first1=D. P.
 |year=1972
 |title=Cooling and Evolution of a Supernova Remnant
 |journal=Astrophysical Journal
 |volume=178 |page=159
 |bibcode=1972ApJ...178..159C
 |doi=10.1086/151775
|doi-access=free
 }}</ref>

[[Image:STScl-2005-15.png|thumb|upright=1.2|Supernova remnant N 63A lies within a clumpy region of gas and dust in the [[Large Magellanic Cloud]].]]
The [[Big Bang]] produced hydrogen, [[helium]] and traces of [[lithium]], while all heavier elements are synthesised in stars, supernovae, and collisions between neutron stars (thus being indirectly due to supernovae). Supernovae tend to enrich the surrounding interstellar medium with elements other than hydrogen and helium, which usually astronomers refer to as "metals".<ref name="Johnson2019">{{Cite journal |last=Johnson |first=Jennifer A. |date=February 2019 |title=Populating the periodic table: Nucleosynthesis of the elements |journal=Science |language=en |volume=363 |issue=6426 |pages=474–478 |doi=10.1126/science.aau9540 |pmid=30705182 |bibcode=2019Sci...363..474J |s2cid=59565697 |issn=0036-8075|doi-access=free }}</ref> These ejected elements ultimately enrich the [[molecular cloud]]s that are the sites of star formation.<ref>
{{cite journal
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 |doi=10.1088/0004-637X/696/2/2138
|s2cid=8703787
 }}</ref> Thus, each stellar generation has a slightly different composition, going from an almost pure mixture of hydrogen and helium to a more metal-rich composition. Supernovae are the dominant mechanism for distributing these heavier elements, which are formed in a star during its period of nuclear fusion. The different abundances of elements in the material that forms a star have important influences on the star's life,<ref name="Johnson2019"/><ref>{{Cite journal |last1=Salaris |first1=Maurizio |last2=Cassisi |first2=Santi |date=August 2017 |title=Chemical element transport in stellar evolution models |doi-access=free |journal=Royal Society Open Science |language=en |volume=4 |issue=8 |article-number=170192 |doi=10.1098/rsos.170192 |pmid=28878972 |pmc=5579087 |bibcode=2017RSOS....470192S |arxiv=1707.07454 |issn=2054-5703}}</ref> and may influence the possibility of having [[planet]]s orbiting it: more [[giant planet]]s form around stars of higher metallicity.<ref>{{cite journal|last1=Fischer |first1=Debra A. |last2=Valenti |first2=Jeff |title=The planet-metallicity correlation |journal=The Astrophysical Journal |bibcode=2005ApJ...622.1102F |doi=10.1086/428383 |volume=622 |year=2005 |issue=2 |pages=1102–1117|s2cid=121872365 |doi-access=free }}</ref><ref>{{cite journal|doi=10.1146/annurev-astro-112420-020055 |bibcode=2021ARA&A..59..291Z |arxiv=2103.02127 |title=Exoplanet Statistics and Theoretical Implications |journal=Annual Review of Astronomy and Astrophysics |volume=59 |year=2021 |last1=Zhu |first1=Wei |last2=Dong |first2=Subo |pages=291–336|s2cid=232105177 }}</ref>

The kinetic energy of an expanding supernova remnant can trigger star formation by compressing nearby, dense molecular clouds in space.<ref>
{{cite journal
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 |journal=From Darkness to Light: Origin and Evolution of Young Stellar Clusters 
 |volume=243 |page=791 
 |doi=10.1051/0004-6361:20021634 
 |arxiv=astro-ph/0008013
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}}</ref> The increase in turbulent pressure can also prevent star formation if the cloud is unable to lose the excess energy.<ref name="aaa128">
{{cite journal
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Evidence from daughter products of short-lived [[radioactive isotope]]s shows that a nearby supernova helped determine the composition of the [[Solar System]] 4.5&nbsp;billion years ago, and may even have triggered the formation of this system.<ref>
{{cite journal
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 |last2=Truran |first2=J.W.
 |year=1977
 |title=The supernova trigger for formation of the solar system
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 |volume=30 |issue=3 |page=447
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[[Fast radio burst]]s (FRBs) are intense, transient pulses of radio waves that typically last no more than milliseconds. Many explanations for these events have been proposed; [[magnetar]]s produced by core-collapse supernovae are leading candidates.<ref name="AJL-20200601">{{cite journal |author=Bhandan, Shivani |date=1 June 2020 |title=The Host Galaxies and Progenitors of Fast Radio Bursts Localised with the Australian Square Kilometre Array Pathfinder |journal=[[The Astrophysical Journal Letters]] |volume=895 |pages=L37 |arxiv=2005.13160 |bibcode=2020ApJ...895L..37B |doi=10.3847/2041-8213/ab672e |s2cid=218900539 |number=2 |doi-access=free }}</ref><ref>{{Cite journal |last=Zhang |first=Bing |date=2020-11-05 |title=The physical mechanisms of fast radio bursts |url=https://www.nature.com/articles/s41586-020-2828-1 |journal=Nature |language=en |volume=587 |issue=7832 |pages=45–53 |doi=10.1038/s41586-020-2828-1 |pmid=33149290 |arxiv=2011.03500 |bibcode=2020Natur.587...45Z |s2cid=226259246 |issn=0028-0836}}</ref><ref>{{Cite web |last=Chu |first=Jennifer |date=2022-07-13 |title=Astronomers detect a radio "heartbeat" billions of light-years from Earth |url=https://news.mit.edu/2022/astronomers-detect-radio-heartbeat-billions-light-years-earth-0713 |access-date=2023-03-19 |website=MIT News |publisher=[[Massachusetts Institute of Technology]] |language=en}}</ref><ref>{{Cite journal |last1=Petroff |first1=E. |last2=Hessels |first2=J. W. T. |last3=Lorimer |first3=D. R. |date=2022-03-29 |title=Fast radio bursts at the dawn of the 2020s |journal=The Astronomy and Astrophysics Review |language=en |volume=30 |issue=1 |page=2 |doi=10.1007/s00159-022-00139-w |arxiv=2107.10113 |bibcode=2022A&ARv..30....2P |s2cid=253690001 |issn=1432-0754}}</ref>

===Cosmic rays===
Supernova remnants are thought to accelerate a large fraction of galactic primary [[cosmic ray]]s, but direct evidence for cosmic ray production has only been found in a small number of remnants. Gamma rays from [[pion]]-decay have been detected from the supernova remnants [[IC 443]] and W44. These are produced when accelerated [[proton]]s from the remnant impact on interstellar material.<ref name="ackermann-2013">
{{cite journal
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 |journal=[[Science (journal)|Science]]
 |volume=339 |issue=6121 |pages=807–11
 |year=2013
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|s2cid=29815601
 }}</ref>

===Gravitational waves===
Supernovae are potentially strong galactic sources of [[gravitational wave]]s,<ref>
{{Cite journal
 |last1=Ott |first1=C. D.
 |last2=O'Connor |first2=E. P.
 |last3=Gossan |first3=S. E.
 |last4=Abdikamalov |first4=E.
 |last5=Gamma |first5=U. C. T.
 |last6=Drasco |first6=S.
 |year=2012
 |title=Core-Collapse Supernovae, Neutrinos, and Gravitational Waves
 |journal=[[Nuclear Physics B: Proceedings Supplements]]
 |volume=235 |pages=381–387
 |arxiv=1212.4250
 |bibcode=2013NuPhS.235..381O
 |doi=10.1016/j.nuclphysbps.2013.04.036
|s2cid=34040033
 }}</ref> but none have so far been detected. The only gravitational wave events so far detected are from mergers of black holes and neutron stars, probable remnants of supernovae.<ref name=morozova>{{cite journal|bibcode=2018ApJ...861...10M|doi=10.3847/1538-4357/aac5f1|title=The Gravitational Wave Signal from Core-collapse Supernovae|journal=The Astrophysical Journal|volume=861|issue=1|page=10|year=2018|last1=Morozova|first1=Viktoriya|last2=Radice|first2=David|last3=Burrows|first3=Adam|last4=Vartanyan|first4=David|arxiv=1801.01914|s2cid=118997362 |doi-access=free }}</ref> Like the neutrino emissions, the gravitational waves produced by a core-collapse supernova are expected to arrive without the delay that affects light. Consequently, they may provide information about the core-collapse process that is unavailable by other means. Most gravitational-wave signals predicted by supernova models are short in duration, lasting less than a second, and thus difficult to detect. Using the arrival of a neutrino signal may provide a trigger that can identify the time window in which to seek the gravitational wave, helping to distinguish the latter from background noise.<ref>{{Cite journal |last1=Al Kharusi |first1=S. |last2=BenZvi |first2=S. Y. |last3=Bobowski |first3=J. S. |last4=Bonivento |first4=W. |last5=Brdar |first5=V. |last6=Brunner |first6=T. |last7=Caden |first7=E. |last8=Clark |first8=M. |last9=Coleiro |first9=A. |last10=Colomer-Molla |first10=M. |last11=Crespo-Anadón |first11=J. I. |last12=Depoian |first12=A. |last13=Dornic |first13=D. |last14=Fischer |first14=V. |last15=Franco |first15=D. |display-authors=14 |date=2021-03-01 |title=SNEWS 2.0: a next-generation supernova early warning system for multi-messenger astronomy |url=https://iopscience.iop.org/article/10.1088/1367-2630/abde33 |journal=New Journal of Physics |volume=23 |issue=3 |page=031201 |doi=10.1088/1367-2630/abde33 |arxiv=2011.00035 |bibcode=2021NJPh...23c1201A |s2cid=226227393 |issn=1367-2630}}</ref>

===Effect on Earth===
{{Main|Near-Earth supernova}}
A near-Earth supernova is a supernova close enough to the Earth to have noticeable effects on its [[biosphere]]. Depending upon the type and energy of the supernova, it could be as far as 3,000 light-years away.
In 1996 it was theorised that traces of past supernovae might be detectable on Earth in the form of metal isotope signatures in [[rock strata]]. [[Iron#Isotopes|Iron-60]] enrichment was later reported in deep-sea rock of the [[Pacific Ocean]].<ref>
{{cite journal
 |last1=Fields |first1=B. D.
 |last2=Hochmuth |first2=K. A.
 |last3=Ellis |first3=J.
 |year=2005
 |title=Deep-Ocean Crusts as Telescopes: Using Live Radioisotopes to Probe Supernova Nucleosynthesis
 |journal=The Astrophysical Journal
 |volume=621 |issue=2 |pages=902–907
 |arxiv=astro-ph/0410525
 |bibcode=2005ApJ...621..902F
 |doi=10.1086/427797
|s2cid=17932224
 }}</ref><ref>{{Cite journal
 |last1=Knie
 |first1=K.
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 |first2=G.
 |last3=Faestermann
 |first3=T.
 |last4=Dorfi
 |first4=E.
 |last5=Rugel
 |first5=G.
 |last6=Wallner
 |first6=A.
 |date=2004
 |title=<sup>60</sup>Fe Anomaly in a Deep-Sea Manganese Crust and Implications for a Nearby Supernova Source
 |journal=[[Physical Review Letters]]
 |volume=93
 |issue=17
 |pages=171103–171106
 |bibcode=2004PhRvL..93q1103K
 |pmid=15525065
 |doi=10.1103/PhysRevLett.93.171103
 |s2cid=23162505
 }}</ref><ref name="Fields">
{{Cite journal
 |last1=Fields |first1=B. D.
 |last2=Ellis |first2=J.
 |date=1999
 |title=On Deep-Ocean Fe-60 as a Fossil of a Near-Earth Supernova
 |journal=[[New Astronomy (journal)|New Astronomy]]
 |volume=4 |issue=6 |pages=419–430
 |arxiv=astro-ph/9811457
 |bibcode=1999NewA....4..419F
 |doi=10.1016/S1384-1076(99)00034-2
|s2cid=2786806
 }}</ref> In 2009, elevated levels of nitrate ions were found in Antarctic ice, which coincided with the 1006 and 1054 supernovae. Gamma rays from these supernovae could have boosted atmospheric levels of nitrogen oxides, which became trapped in the ice.<ref>
{{cite journal
 |year=2009
 |title=In Brief
 |journal=Scientific American
 |volume=300 |issue=5 |page=28
 |bibcode=2009SciAm.300e..28.
 |doi=10.1038/scientificamerican0509-28a
}}</ref>

Historically, nearby supernovae may have influenced the [[biodiversity]] of life on the planet. Geological records suggest that nearby supernova events have led to an increase in cosmic rays, which in turn produced a cooler climate. A greater temperature difference between the poles and the equator created stronger winds, increased ocean mixing, and resulted in the transport of [[nutrients]] to shallow waters along the [[continental shelves]]. This led to greater biodiversity.<ref>{{cite news
 | title=Did Supernovae Help Push Life to Become More Diverse?
 | first=Carolyn Collins | last=Petersen
 | work=Universe Today | date=March 22, 2023
 | url=https://www.universetoday.com/160686/did-supernovae-help-push-life-to-become-more-diverse/
 | access-date=2023-03-23
}}</ref><ref>{{cite journal
 | title=A persistent influence of supernovae on biodiversity over the Phanerozoic
 | first=Henrik | last=Svensmark | author-link=Henrik Svensmark
 | journal=Ecology and Evolution
 | volume=13 | issue=3 | id=e9898 | date=March 16, 2023
 | article-number=e9898 | publisher=Wiley Online Library | doi=10.1002/ece3.9898
| pmid=36937070 | pmc=10019915 | bibcode=2023EcoEv..13E9898S }}</ref>

Type Ia supernovae are thought to be potentially the most dangerous if they occur close enough to the Earth. Because these supernovae arise from dim, common white dwarf stars in binary systems, it is likely that a supernova that can affect the Earth will occur unpredictably and in a star system that is not well studied. The closest-known candidate is [[IK Pegasi]] (HR 8210), about 150 light-years away,<ref>
{{Cite journal
 |last=Gorelick |first=M.
 |date=2007
 |title=The Supernova Menace
 |journal=[[Sky & Telescope]]
 |volume=113 |issue=3 |page=26
 |bibcode=2007S&T...113c..26G
}}</ref><ref>
{{Cite journal |last1=Landsman |first1=W. |last2=Simon |first2=T. |last3=Bergeron |first3=P. |date=1999 |title=The hot white-dwarf companions of HR 1608, HR 8210, and HD 15638 |journal=[[Publications of the Astronomical Society of the Pacific]] |volume=105 |issue=690 |pages=841–847 |bibcode=1993PASP..105..841L |doi=10.1086/133242 |doi-access=free}}</ref> but observations suggest that it could be as long as 1.9&nbsp;billion years before the white dwarf can accrete the critical mass required to become a Type Ia supernova.<ref>{{Cite journal |last=Beech |first=Martin |date=December 2011 |title=The past, present and future supernova threat to Earth's biosphere |url=http://link.springer.com/10.1007/s10509-011-0873-9 |journal=Astrophysics and Space Science |language=en |volume=336 |issue=2 |pages=287–302 |bibcode=2011Ap&SS.336..287B |doi=10.1007/s10509-011-0873-9 |issn=0004-640X |s2cid=119803426|url-access=subscription }}</ref> 

According to a 2003 estimate, a Type II supernova would have to be closer than {{Convert|8|pc|lk=in|abbr=off}} to destroy half of the Earth's ozone layer, and there are no such candidates closer than about 500 light-years.<ref name="Gehrels">
{{Cite journal
 |last1=Gehrels |first1=N.
 |last2=Laird |first2=C. M.
 |last3=Jackman |first3=C. H.
 |last4=Cannizzo |first4=J. K.
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 |last6=Chen |first6=W.
 |date=2003
 |title=Ozone Depletion from Nearby Supernovae
 |journal=[[Astrophysical Journal]]
 |volume=585|issue=2 |pages=1169–1176
 |arxiv=astro-ph/0211361
 |bibcode=2003ApJ...585.1169G
 |doi=10.1086/346127
|s2cid=15078077
 }}</ref>

==Milky Way candidates==
{{Main|List of supernova candidates}}
[[Image:Wolf rayet2.jpg|thumb|The [[Wolf–Rayet nebula|nebula]] around [[Wolf–Rayet star]] WR124, which is located at a distance of about 21,000 [[light-year]]s<ref>
{{cite journal
 |last1=Van Der Sluys |first1=M. V.
 |last2=Lamers |first2=H. J. G. L. M.
 |year=2003
 |title=The dynamics of the nebula M1-67 around the run-away Wolf-Rayet star WR 124
 |journal=Astronomy and Astrophysics
 |volume=398 |pages=181–194
 |arxiv=astro-ph/0211326
 |bibcode=2003A&A...398..181V
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|s2cid=6142859
 }}</ref>]]

The next supernova in the Milky Way will likely be detectable even if it occurs on the far side of the galaxy. It is likely to be produced by the collapse of an unremarkable red supergiant, and it is very probable that it will already have been catalogued in infrared surveys such as [[2MASS]]. There is a smaller chance that the next core collapse supernova will be produced by a different type of massive star such as a yellow hypergiant, luminous blue variable, or Wolf–Rayet. The chances of the next supernova being a Type Ia produced by a white dwarf are calculated to be about a third of those for a core collapse supernova. Again it should be observable wherever it occurs, but it is less likely that the progenitor will ever have been observed. It is not even known exactly what a Type Ia progenitor system looks like, and it is difficult to detect them beyond a few parsecs. The total supernova rate in the Milky Way is estimated to be between 2 and 12 per century, although one has not actually been observed for several centuries.<ref name="adams">
{{cite journal
 |last1=Adams |first1=S. M.
 |last2=Kochanek |first2=C. S.
 |last3=Beacom |first3=J. F.
 |last4=Vagins |first4=M. R.
 |last5=Stanek |first5=K. Z.
 |year=2013
 |title=Observing the Next Galactic Supernova
 |journal=[[The Astrophysical Journal]]
 |volume=778 |issue=2 |page=164
 |arxiv=1306.0559
 |bibcode=2013ApJ...778..164A
 |doi=10.1088/0004-637X/778/2/164
|s2cid=119292900
 }}</ref>

Statistically, the most common variety of core-collapse supernova is Type II-P, and the progenitors of this type are red supergiants.<ref>{{Cite journal |last1=Cristofari |first1=P |last2=Marcowith |first2=A |last3=Renaud |first3=M |last4=Dwarkadas |first4=V V |last5=Tatischeff |first5=V |last6=Giacinti |first6=G |last7=Peretti |first7=E |last8=Sol |first8=H |date=2022-02-18 |title=The first days of Type II-P core collapse supernovae in the gamma-ray range |url=https://academic.oup.com/mnras/article/511/3/3321/6517473 |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=511 |issue=3 |pages=3321–3329 |doi=10.1093/mnras/stac217 |doi-access=free |issn=0035-8711|arxiv=2201.09583 }}</ref> It is difficult to identify which of those supergiants are in the final stages of heavy element fusion in their cores and which have millions of years left. The most-massive red supergiants shed their atmospheres and evolve to Wolf–Rayet stars before their cores collapse. All Wolf–Rayet stars end their lives from the Wolf–Rayet phase within a million years or so, but again it is difficult to identify those that are closest to core collapse. One class that is expected to have no more than a few thousand years before exploding are the WO Wolf–Rayet stars, which are known to have exhausted their core helium.<ref>
{{cite journal
 |last1=Tramper |first1=F.
 |last2=Straal |first2=S. M.
 |last3=Sanyal |first3=D.
 |last4=Sana |first4=H.
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 |last6=Gräfener |first6=G.
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 |last8=Vink |first8=J. S.
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 }}</ref> Only eight of them are known, and only four of those are in the Milky Way.<ref name=tramper>
{{cite journal
 |last1=Tramper |first1=F.
 |last2=Gräfener |first2=G.
 |last3=Hartoog |first3=O. E.
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 |year=2013
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A number of close or well-known stars have been identified as possible core collapse supernova candidates: the high-mass blue stars [[Spica]], [[Rigel]] and [[Deneb]],<ref>{{Cite journal |last=Firestone |first=R. B. |date=June 2014 |title=Observation of 23 Supernovae That Exploded <300 pc from Earth during the past 300 kyr|journal=The Astrophysical Journal |language=en |volume=789 |issue=1 |page=29 |bibcode=2014ApJ...789...29F |doi=10.1088/0004-637X/789/1/29 |issn=0004-637X}}</ref> the red supergiants [[Betelgeuse]], [[Antares]], and [[VV Cephei|VV Cephei A]];<ref>
{{cite book
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{{cite journal
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}}</ref> the luminous blue variable Eta Carinae that has already produced a supernova impostor;<ref>
{{cite journal
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 |last3=Schöller |first3=M.
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 |year=2003
 |title=Direct measurement of the size and shape of the present-day stellar wind of eta Carinae
 |journal=Astronomy and Astrophysics
 |volume=410 |issue=3 |pages=L37
 |arxiv=astro-ph/0310399
 |bibcode=2003A&A...410L..37V
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|s2cid=18163131
 }}</ref> and both components, a blue supergiant and a Wolf–Rayet star, of the Regor or [[Gamma Velorum]] system.<ref>
{{cite book
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 |bibcode=2011LNP...812..153T
 |s2cid=119254840
 }}</ref><ref>{{Cite web |title=Regor |url=http://stars.astro.illinois.edu/sow/regor.html |access-date=2024-08-18 |website=stars.astro.illinois.edu}}</ref> [[Mimosa (star)|Mimosa]], [[Acrux]] and Hadar or [[Beta Centauri]], three bright star systems in the southern constellation of [[Crux]] and [[Centaurus]] respectively, each contain blue stars with sufficient masses to explode as supernovae.<ref>{{Cite web |title=Acrux |url=http://stars.astro.illinois.edu/sow/acrux.html |access-date=2024-08-15 |website=stars.astro.illinois.edu}}</ref><ref>{{Cite web |title=Mimosa |url=http://stars.astro.illinois.edu/sow/mimosa.html |access-date=2024-08-15 |website=stars.astro.illinois.edu}}</ref><ref>{{Cite web| title=Hadar |url=http://stars.astro.illinois.edu/sow/hadar.html |access-date=2025-03-12 |website=stars.astro.illinois.edu}}</ref> Others have gained notoriety as possible, although not very likely, progenitors for a gamma-ray burst; for example [[WR 104]].<ref>
{{cite journal
 |last1=Tuthill |first1=P. G.
 |last2=Monnier |first2=J. D.
 |last3=Lawrance |first3=N.
 |last4=Danchi |first4=W. C.
 |last5=Owocki |first5=S. P.
 |last6=Gayley |first6=K. G.
 |year=2008
 |title=The Prototype Colliding-Wind Pinwheel WR 104
 |journal=The Astrophysical Journal
 |volume=675 |issue=1 |pages=698–710
 |arxiv=0712.2111
 |doi=10.1086/527286
 |bibcode=2008ApJ...675..698T
|s2cid=119293391
 }}</ref>

Identification of candidates for a Type Ia supernova is much more speculative. Any binary with an accreting white dwarf might produce a supernova, although the exact mechanism and timescale is still debated. These systems are faint and difficult to identify, but the novae and [[recurrent nova]]e are such systems that conveniently advertise themselves. One example is [[U&nbsp;Scorpii]].<ref>
{{cite conference
 |last1=Thoroughgood |first1=T. D.
 | last2=Dhillon | first2=V. S.
 | last3=Littlefair | first3=S. P.
 | last4=Marsh | first4=T. R.
 | last5=Smith | first5=D. A.
 |date=2002
 |title=The recurrent nova U Scorpii – A type Ia supernova progenitor
 |book-title=The Physics of Cataclysmic Variables and Related Objects
 |volume=261
 |location=San Francisco, CA
 |publisher=[[Astronomical Society of the Pacific]]
 |arxiv=astro-ph/0109553
 |bibcode=2002ASPC..261...77T
}}</ref>

[[File:Supernova candidates.jpg|center|thumb|681x681px|Some of the closest core-collapse supernova candidates to Earth within one kiloparsec, most of which are K-type red supergiants<ref name=":2">{{Cite journal |last1=Mukhopadhyay |first1=Mainak |last2=Lunardini |first2=Cecilia |last3=Timmes |first3=F. X. |last4=Zuber |first4=Kai |date=2020-08-01 |title=Presupernova neutrinos: directional sensitivity and prospects for progenitor identification |journal=The Astrophysical Journal |volume=899 |issue=2 |page=153 |doi=10.3847/1538-4357/ab99a6 |doi-access=free |arxiv=2004.02045 |bibcode=2020ApJ...899..153M |issn=0004-637X}}</ref>]]
{{clear}}

==See also==
* {{annotated link|Kilonova}}
* [[List of supernovae]]
* [[List of supernova remnants]]
* [[List of supernova candidates]]
* {{annotated link|Quark-nova}}
* {{annotated link|Superluminous supernova}}
* {{annotated link|Failed supernova}}
* {{annotated link|Supernovae in fiction}}
* {{annotated link|Timeline of white dwarfs, neutron stars, and supernovae}}
* {{annotated link|Collapsar}}
* {{annotated link|Hypernova}}

==References==
{{Reflist}}

==Further reading==
* {{cite book |url=https://link.springer.com/referencework/10.1007/978-3-319-21846-5 |title=Handbook of Supernovae |editor1=Athem W. Alsabti |editor2=Paul Murdin |isbn=978-3-319-21845-8 |date=2017 |publisher=Springer Cham|doi=10.1007/978-3-319-21846-5 |bibcode=2017hsn..book.....A }}
* {{cite book
 |last1=Branch |first1=D.
 |last2=Wheeler |first2=J. C.
 |date=2017
 |title=Supernova Explosions
 |publisher=Springer
 |isbn=978-3-662-55052-6
 |page=721
|ref=none}} 
* {{cite book|title=Nuclear Physics of Stars, 2nd ed. |last=Iliadis |first=Christian |year=2015 |isbn=978-3-527-69266-8 |publisher=Wiley-VCH |location=Weinheim |url=https://onlinelibrary.wiley.com/doi/book/10.1002/9783527692668 |doi=10.1002/9783527692668}}
* {{cite journal
 |last1=Takahashi |first1=K.
 |last2=Sato |first2=K.
 |last3=Burrows |first3=A.
 |last4=Thompson |first4=T. A.
 |date=2003
 |title=Supernova Neutrinos, Neutrino Oscillations, and the Mass of the Progenitor Star
 |journal=[[Physical Review D]]
 |volume=68 |issue=11 |pages=77–81
 |arxiv=hep-ph/0306056
 |doi=10.1103/PhysRevD.68.113009
|bibcode=2003PhRvD..68k3009T|s2cid=119390151
 |ref=none}}
* {{cite journal
 |last1=Woosley |first1=S. E.
 |last2=Janka |first2=H.-T.
 |date=2005
 |title=The Physics of Core-Collapse Supernovae
 |journal=[[Nature Physics]]
 |volume=1 |issue=3 |pages=147–154
 |arxiv=astro-ph/0601261
 |doi=10.1038/nphys172 |bibcode=2005NatPh...1..147W|citeseerx=10.1.1.336.2176
|s2cid=118974639
 |ref=none}}

==External links==
{{Commons category|Supernovae}}
* {{cite web
 |last1=Tsvetkov |first1=D. Yu.
 |last2=Pavlyuk |first2=N. N.
 |last3=Bartunov |first3=O. S.
 |last4=Pskovskii |first4=Y. P.
 |title=Sternberg Astronomical Institute Supernova Catalogue
 |url=http://www.sai.msu.su/sn/sncat/
 |publisher=[[Sternberg Astronomical Institute]], [[Moscow University]]
 |access-date=28 November 2006
|ref=none}} A searchable catalogue
* {{cite web
 |title=The Open Supernova Catalog |website=[[GitHub]]
|date=6 October 2022
|url=https://github.com/astrocatalogs/supernovae
}} An open-access catalog of supernova light curves and spectra.
* {{cite web
 |title=List of Supernovae with IAU Designations
|url=http://www.cbat.eps.harvard.edu/lists/RecentSupernovae.html
 |publisher=[[International Astronomical Union|IAU: Central Bureau for Astronomical Telegrams]]
 |access-date=25 October 2010
|ref=none}}

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