View source for NGC 6240

{{Short description|Galaxy merger remnant in the constellation Ophiuchus}}
{{Sky|16|52|58.8708|+|02|24|03.333}}
{{Infobox Galaxy
| name = [[New General Catalogue|NGC]] 6240
| image = Hubble revisits tangled NGC 6240.jpg
| caption = NGC 6240 imaged by the [[Hubble Space Telescope]]. At the centre there are two supermassive black holes spiraling closer and closer to one another.<ref>{{cite web|title=Hubble revisits tangled NGC 6240|url=https://www.spacetelescope.org/images/potw1520a/|access-date=12 June 2015}}</ref>
| epoch = [[J2000]]
| type = I0 pec<ref name="ned">{{cite web
  | website=NASA/IPAC Extragalactic Database
  | title=Results for object NGC 6240
  | url=https://ned.ipac.caltech.edu/byname?objname=NGC+6240
  | access-date=2025-05-07}}</ref>
| ra = {{RA|16|52|58.8708}}<ref name="ned" />
| dec = {{DEC|+02|24|03.333}}<ref name="ned" />
| dist_ly = {{convert|107.90 ± 7.56|Mpc|Mly|abbr=on|lk=on|order=flip}}{{r|ned}}
| z = 7287 ± 8 km/[[second|s]]<ref name="ned" />
| appmag_v = 12.8<ref name="ned" />
| size_v = {{Val|2.1|×|1.1|u=arcminute}}{{r|ned}}
| size = ~{{convert|74.48|kpc|ly|abbr=on|lk=on|order=flip}} (estimated){{r|ned}}
| constellation name = [[Ophiuchus]]
| notes = merger remnant
| names = {{odlist | IC= 4625 | UGC= 10592 | PGC= 59186 | VV= 617 | CGCG= 025-011 | MCG= +00-43-004 | IRAS= 16504+0228}}<ref name="ned" />
}}

'''NGC 6240''', also known as the '''Starfish Galaxy''', is a nearby [[ultraluminous infrared galaxy]] (ULIRG) in the [[constellation]] [[Ophiuchus]]. It was discovered by [[France|French]] astronomer [[Édouard Stephan]] on 12 July 1871.<ref name="selig">{{cite web | url = https://cseligman.com/text/atlas/ngc62.htm#6240 | title = New General Catalogue Objects: NGC{{nbsp}}6240 | last = Seligman | first = Courtney | website = Celestial Atlas | access-date = 28 August 2024 }}</ref>

The galaxy is the remnant of a [[Galaxy merger|merger]] between three smaller galaxies. The collision between the three progenitor galaxies has resulted in a single, larger galaxy with three distinct nuclei and a highly disturbed structure, including faint extensions and loops.<ref name="friedschulz1983">
{{cite journal
 | last1  = Fried  | first1  = J. W.
 | last2 = Schulz | first2 = H.
 | date    = 1983
 | title   = NGC 6240 – A unique interacting galaxy
 | journal = [[Astronomy and Astrophysics]]
 | volume  = 118
 | pages   = 166–170
 | bibcode = 1983A&A...118..166F
}}</ref>

==Double nuclei==

===Star formation versus supermassive black holes===
The power sources of ULIRGs in general has been greatly debated. Infrared light from galaxies generally originates from dust in the [[interstellar medium]]. ULIRGs are abnormally bright in the infrared. The infrared dust emission in ULIRGs is over one trillion times more luminous than the [[Sun]] (i.e. it has an infrared luminosity of {{Solar luminosity|10<sup>12</sup>}}). Astronomers have speculated that either intense [[star formation]] regions or [[Active galactic nucleus|active galactic nuclei]] (which contain [[supermassive black hole]]s) may be responsible for the intense dust heating that produces this emission, although the general consensus is that both may be present in most ULIRGs. Studying the exact nature of ULIRGs has been difficult, however, because the dust in the centers of these galaxies obscures both visible and near-infrared starlight and because theoretical models of both [[starburst galaxy|starbursts]] and active galactic nuclei have demonstrated that they may look similar. Because NGC 6240 is a nearby example of such a ULIRG, astronomers have studied it intensively to understand its power source.{{Citation needed|date=June 2019}}

===X-ray observations===
[[Image:Ngc6240 chandra.jpg|250px|thumb|left|X-ray image of NGC 6240 taken with the [[Chandra X-Ray Observatory]], superimposed on an optical image of the galaxy. The X-ray emission from the two [[Active galactic nucleus|active galactic nuclei]] can be seen as bright blue point sources. Credit: [[NASA]]]]

Observations performed by [[Stefanie Komossa]] and collaborators with the [[Chandra X-Ray Observatory]] have detected strong hard [[X-ray]] emission from two of the nuclei. The intensity of this emission and the presence of emission from lowly [[ion]]ized or neutral [[iron]] indicate that both of these nuclei are [[active galactic nuclei]].<ref name="komossaetal2003">
{{cite journal
 | last1  = Komossa  | first1  = Stefanie
 | last2 = Burwitz  | first2 = Vadim
 | last3 = Hasinger | first3 = Guenther
 | last4 = Predehl  | first4 = Peter
 | last5 = Kaastra  | first5 = Jelle S.
 | last6 = Ikebe    | first6 = Yasushi
 | display-authors = 4
 | title           = Discovery of a Binary Active Galactic Nucleus in the Ultraluminous Infrared Galaxy NGC 6240 Using Chandra
 | date            = 2003
 | journal         = [[Astrophysical Journal]]
 | volume          = 582
 | issue           = 1
 | pages           = L15–L19
 | arxiv           = astro-ph/0212099
 | bibcode         = 2003ApJ...582L..15K
 | doi             = 10.1086/346145
| s2cid = 16697327
 }}</ref>
Presumably, these are the black holes that were originally at the centers of the merging galaxies. Over the course of millions of years, the black holes are expected to come closer together and form a [[binary black hole|binary supermassive black hole]].{{Citation needed|date=June 2019}}
{{Clear}}

Recent studies by Wolfram Kollatschny and collaborators using the MUSE instrument on board the [[Very Large Telescope|VLT]] have revealed that there are in fact three, not two, supermassive black holes at the core of this remnant. Their masses are suggested to be 90 million, 710 million, and 360 million solar masses.<ref name="kollatschny2020">{{Cite Q| Q105750544|author1=Kollatschny, W|author2=Weilbacher, P|author3=Ochmann, M|author4=Chelouche, D|display-authors=3}}</ref> Two of the three black holes are active. The additional SMBH implies that three original galaxies are merging instead of two.

== Supernovae ==
Four [[supernova]]e have been observed in NGC 6240:
* '''SN 2000bg''' ([[Type II supernova#Type_IIn_supernovae|Type{{nbsp}}IIn]], mag. 17.4) was discovered by the [[Lick Observatory]] Supernova Search (LOSS) on 1 April  2000.<ref>{{cite journal | bibcode=2000IAUC.7392....1S | title = Supernova 2000bg in NGC 6240 | last1= Sato | first1= Y. | last2= Li | first2= W. D. | journal = International Astronomical Union Circular | date = 2000 | issue = 7392 | page = 1 | url=http://www.cbat.eps.harvard.edu/iauc/07300/07392.html#Item1}}</ref><ref>{{cite web | website=Transient Name Server | title=SN{{nbsp}}2000bg | url=https://www.wis-tns.org/object/2000bg | publisher = [[International Astronomical Union|IAU]] | access-date=7 May 2025}}</ref>
* '''SN 2010gp''' ([[type Ia supernova|Type&nbsp;Ia]], mag. 17.5) was discovered by The CHilean Automatic Supernova sEarch (CHASE) on 14 July 2010.<ref>{{cite journal | last=Maza | first=J. | date=July 2010 | editor-last=Green | editor-first=D. W. E. | title=Supernova 2010gp in NGC 6240 | journal=Central Bureau Electronic Telegrams | issue=2388 | page=1 | bibcode=2010CBET.2388....1M | url= http://www.cbat.eps.harvard.edu/iau/cbet/002300/CBET002388.txt}}</ref><ref>{{cite web | website=Transient Name Server | title=SN{{nbsp}}2010gp | url=https://www.wis-tns.org/object/2010gp | publisher = [[International Astronomical Union|IAU]] | access-date=7 May 2025}}</ref>
* '''SN 2013dc''' ([[Type II supernova#Light_curves_for_Type_II-L_and_Type_II-P_supernovae|Type II-P]], mag. 18.7) was discovered by [[Adam Block (astrophotographer)|Adam Block]] on 11 April 2013.<ref>{{cite journal | last=Block | first=Adam | date=2013 | editor-last=Green | editor-first=D. W. E. | title=Supernova 2013dc in NGC 6240 = Psn J16525897+0224255 | journal=Central Bureau Electronic Telegrams | issue=3551 | page=1 | bibcode=2013CBET.3551....1B }}</ref><ref>{{cite web | website=Transient Name Server | title=SN{{nbsp}}2013dc | url=https://www.wis-tns.org/object/2013dc | publisher = [[International Astronomical Union|IAU]] | access-date=7 May 2025}}</ref>
* '''PSN J16525760+0223367''' (Type Ia, mag. 15.8) was discovered by Robert Gagliano, [[Jack B. Newton|Jack Newton]], and [[Puckett Observatory#Tim_Puckett|Tim Puckett]] on 23 April 2014.<ref>[https://www.rochesterastronomy.org/sn2014/index.html#PSNJ16525760+0223367 Bright Supernovae – 2014] Retrieved 25 March 2023.</ref>

== Final stages ==
A [[galaxy merger]] is a slow process lasting more than a billion years as two galaxies, under the inexorable pull of gravity, dance toward each other before finally joining together. After research done over the past few years, scientists have concluded that this galaxy has reached its last stages before colliding into one another. Photographic evidence proves that the two nuclei have been growing closer, and in that process, they have been emitting more gasses and [[stellar wind]]s outward. Those winds evict about 100 solar masses in gases from the galaxy every year. This type of winds and growth of the black holes are known to occur during the last 10 to 20 million years of the merger; it is assumed that this is the amount of time left for the galaxy to finish its collision phase. <ref>{{Cite news|url=https://www.nasa.gov/feature/goddard/2018/astronomers-unveil-growing-black-holes-in-colliding-galaxies|title=Astronomers Unveil Growing Black Holes in Colliding Galaxies|date=2018-11-07|access-date=2018-11-26|archive-url=https://web.archive.org/web/20190615210254/https://www.nasa.gov/feature/goddard/2018/astronomers-unveil-growing-black-holes-in-colliding-galaxies/|archive-date=2019-06-15|url-status=live|publisher=[[NASA]]|editor-last=Hille|editor-first=Karl}}</ref> After this phase, the merged galaxies will become one, becoming a post-merger object until if and when any tidal tails and plumes evaporate.

==Gallery==
<gallery>
File:Hubble and Keck observatories uncover black holes coalescing.tif|Hubble and Keck observatories uncover black holes coalescing.<ref>{{cite web|url=https://www.spacetelescope.org/images/opo1828a/|title=Hubble and Keck observatories uncover black holes coalescing|date=8 November 2018|publisher=[[European Space Agency|ESA]] / [[Hubble Space Telescope]]|archive-url=https://web.archive.org/web/20181108172623/https://www.spacetelescope.org/images/opo1828a/|archive-date=8 November 2018|url-status=live|access-date=8 November 2018}}</ref>
File:Galaxies Gone Wild!.jpg|[[Arp 148]], [[VV 340]], [[Arp 256]], [[NGC 6670]], NGC 6240, [[ESO 593-8]], [[NGC 454]], [[UGC 8335]], [[NGC 6786]], [[NGC 17]], [[ESO 77-14]], [[Arp 272]]
File:Iotw2342c.tiff|NGC 6240 imaged by the [[Cerro Tololo Inter-American Observatory]]
</gallery>

== See also ==
{{Commons}}
* [[Arp 220]] – ''another ultraluminous infrared galaxy and merger remnant''
* [[Antennae Galaxies]] – ''a nearby pair of merging galaxies''
* [[NGC 520]] – ''another merger remnant''
* [[Markarian 273]] – ''an ultraluminous infrared galaxy with two active nuclei''
* [[UGC 5101]] – ''another ultraluminous infrared galaxy with active nucleus''

==References==
{{Reflist|2}}

==External links==
*{{cite journal|last1=Merritt|first1=David|author-link=David Merritt|last2=Milosavljevic|first2=Milos|title=Massive Black Hole Binary Evolution|journal=Living Reviews in Relativity|volume=8|pages=8|date=2005|doi=10.12942/lrr-2005-8|doi-broken-date=1 July 2025 |doi-access=free |arxiv=astro-ph/0410364|bibcode=2005LRR.....8....8M|s2cid=119367453}}
*[https://chandra.harvard.edu/photo/2002/0192/ NGC 6240: Two Supermassive Black Holes in Same Galaxy]

{{Ngc65}}{{ophiuchus}}

{{DEFAULTSORT:NGC 6240}}
[[Category:Irregular galaxies]]
[[Category:Galaxy mergers]]
[[Category:Peculiar galaxies]]
[[Category:Luminous infrared galaxies]]
[[Category:Ophiuchus]]
[[Category:NGC objects|6240]]
[[Category:IC objects]]
[[Category:UGC objects|10592]]
[[Category:Principal Galaxies Catalogue objects|59186]]
[[Category:Discoveries by Édouard Stephan]]
[[Category:Astronomical objects discovered in 1871]]