View source for Messier 15

{{short description|Globular cluster in the constellation Pegasus}}
{{ Infobox globular cluster<!-- put name or coordinates into the following URL -->
| name=Messier 15
| image=[[Image:M15_Globular_Cluster__from_the_Mount_Lemmon_SkyCenter_Schulman_Telescope_courtesy_Adam_Block.jpg|Deep Broadband (RGB) image of M15 from the Mount Lemmon SkyCenter|300px]]
| caption=Deep Broadband (RGB) image of M15
| epoch=[[J2000]]
| class=IV<ref name=hcob849_11/>
| constellation=[[Pegasus (constellation)|Pegasus]]
| ra={{RA|21|29|58.33}}<ref name=aj140_6_1830/>
| dec={{DEC|+12|10|01.2}}<ref name=aj140_6_1830/>
| dist_ly={{cvt|10.944|±|0.131|kpc|kly|order=flip|lk=on}}<ref name=Bhardwaj/>
| appmag_v=6.2<ref>{{cite web |url=http://www.messier.seds.org/m/m015.html |title=Messier 15 |access-date=21 July 2024 |website=SEDS Messier Catalog}}</ref>
| size_v=18′.0
| mass_msol={{Val|5.6|e=5}}<ref name=mnras406_3_2000/>
| radius_ly=~88 ly<ref>distance × sin( diameter_angle / 2 ) = 88 ly radius</ref>
| metal_fe = –2.37<ref name=apj742_1_51/>
| v_hb=15.83
| age=12.0&nbsp;[[Gigayear|Gyr]]<ref name=mnras385_4_1998/>
| notes=steep central cusp
| names=[[New General Catalogue|NGC]] 7078, GCl 120<ref name="simbad" />
}}

'''Messier 15''' or '''M15''' (also designated '''NGC 7078''' and sometimes known as the '''Great Pegasus Cluster''') is a [[globular cluster]] in the [[constellation]] [[Pegasus (constellation)|Pegasus]]. It was discovered by [[Jean-Dominique Maraldi]] in 1746 and included in [[Charles Messier]]'s catalogue of [[comet]]-like objects in 1764.{{cn|date=March 2021}}  At an estimated {{val|12.5|1.3}} billion years old, it is one of the oldest known globular clusters.<ref name="Malley"/>

==Characteristics==
'''M&nbsp;15''' is about 35,700&nbsp;[[light-year]]s from [[Earth]],<ref name=Bhardwaj/> and 175&nbsp;light-years in diameter. It has an [[absolute magnitude]] of &minus;9.2, which translates to a total [[luminosity]] of 360,000&nbsp;times that of the [[Sun]]. Messier&nbsp;15 is one of the most densely packed globulars known in the [[Milky Way galaxy]]. Its core has undergone a contraction known as "[[Core collapse (cluster)|core collapse]]" and it has a central density cusp with an enormous number of stars surrounding what may be a central black hole.<ref name="Gerssen2002">
{{cite journal |vauthors=Gerssen J, van der Marel RP, Gebhardt K, Guhathakurta P, Peterson RC, Pryor C |year=2003 |series=Hubble Space Telescope |title=Evidence for an intermediate-mass black hole in the globular cluster M&nbsp;15. II.&nbsp;Kinematic analysis and dynamical modeling |journal=[[Astronomical Journal]] |volume=125 |issue=1 |pages=376–377 |doi=10.1086/345574 |bibcode=2003AJ....125..376G |arxiv=astro-ph/0210158|s2cid=118948032 }}</ref>

Home to over 100,000&nbsp;stars,the cluster is notable for containing a large number of [[variable star]]s (112) and [[pulsar]]s (8), including one double [[neutron star]] system, M15-C. It also contains [[Pease 1]], the first [[planetary nebula]] discovered within a globular cluster in 1928.<ref name="Gillettetal1989">{{cite journal |author=Cohen, J.G. |author2=Gillett, F.C. |date=1989 |title=The peculiar planetary nebula in M&nbsp;22 |journal=[[Astrophysical Journal]] |volume=346 | pages=803–807 |bibcode=1989ApJ...346..803C |doi=10.1086/168061|s2cid=119770028 |url=https://authors.library.caltech.edu/96075/1/1989ApJ___346__803C.pdf }}</ref><ref name=OMeara1998 /> Just three others have been found in globular clusters since then.<ref>{{cite web |url=http://www.messier.seds.org/more/m015_h2.html |series=Messier&nbsp;15 |title=more |website=SEDS.org}}</ref>

==Amateur astronomy==
At magnitude 6.2, M15 approaches [[naked eye]] visibility under good conditions and can be observed with binoculars or a small telescope, appearing as a fuzzy star.<ref name=OMeara1998 /> Telescopes with a larger aperture (at least 6 in. (150&nbsp;mm)) will start to reveal individual stars, the brightest of which are of [[apparent magnitude|magnitude]] +12.6. The cluster appears 18 arc minutes in size (three tenths of a degree across). M15 is around 4° WNW of the brightest star of Pegasus, [[Epsilon Pegasi]].<ref name=OMeara1998 />

==X-ray sources==
[[Earth-orbiting satellite]]s [[Uhuru (satellite)|Uhuru]] and [[Chandra X-ray Observatory]] have detected two bright X-ray sources in this cluster: Messier 15 X-1 (4U 2129+12) and Messier 15 X-2.<ref name=Forman>
{{cite journal
 |author=Forman W | author2=Jones C | author3=Cominsky L | author4=Julien P | author5=Murray S | author6=Peters G
 |date=1978
 |title=The fourth Uhuru catalog of X-ray sources
 |journal=[[Astrophysical Journal Supplement Series]]
 |volume=38 |page=357
 |doi=10.1086/190561
|bibcode=1978ApJS...38..357F
|doi-access=free}}</ref><ref name=White>
{{ cite journal
 |author=White NE | author2=Angelini L
 |date=2001
 |title=The discovery of a second luminous low-mass X-ray binary in the globular cluster M15
 |journal=[[Astrophysical Journal Letters]]
 |volume=561
 |issue=1 |pages=L101–5
 |bibcode=2001ApJ...561L.101W
 |doi=10.1086/324561
|arxiv = astro-ph/0109359 | s2cid=18877294
 }}</ref> The former appears to be the first [[astronomical X-ray source]] detected in Pegasus.

==Gallery==
<gallery>
Image:M15 core lucky 10pc.gif|The central square arcminute of M15 imaged using the [[lucky imaging]] technique
Image:M15map.png|Map showing the location of M15
Image:New Hubble image of star cluster Messier 15.jpg|M15 photographed by [[Hubble Space Telescope|HST]]. The [[planetary nebula]] [[Pease 1]] can be seen as a small blue object to the upper left of the core of the cluster.
</gallery>

==See also==
* [[List of Messier objects]]
* [[X-ray astronomy]]

==References==
{{reflist|30em|refs=

<ref name=Bhardwaj>{{cite journal | doi=10.3847/1538-4357/ac214d | title=Optical and Near-infrared Pulsation Properties of RR Lyrae and Population II Cepheid Variables in the Messier 15 Globular Cluster | year=2021 | last1=Bhardwaj | first1=Anupam | last2=Rejkuba | first2=Marina | last3=Sloan | first3=G. C. | last4=Marconi | first4=Marcella | last5=Yang | first5=Soung-Chul | journal=The Astrophysical Journal | volume=922 | issue=1 | page=20 | arxiv=2108.11388 | bibcode=2021ApJ...922...20B | s2cid=237304172 | doi-access=free }}</ref>

<ref name=aj140_6_1830>{{Cite journal | display-authors=1 | last1=Goldsbury | first1=Ryan | last2=Richer | first2=Harvey B. | last3=Anderson | first3=Jay | last4=Dotter | first4=Aaron | last5=Sarajedini | first5=Ata | last6=Woodley | first6=Kristin | title=The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters | journal=The Astronomical Journal | volume=140 | issue=6 | pages=1830–1837 |date=December 2010 | doi=10.1088/0004-6256/140/6/1830 | bibcode=2010AJ....140.1830G |arxiv = 1008.2755 | s2cid=119183070 }}</ref>

<ref name="simbad">{{cite simbad | title=M 15 | access-date=2006-11-16 }}</ref>

<ref name=hcob849_11>{{Cite journal | last1=Shapley | first1=Harlow | last2=Sawyer | first2=Helen B. | title=A Classification of Globular Clusters | journal=Harvard College Observatory Bulletin | issue=849 | pages=11–14 |date=August 1927 | bibcode=1927BHarO.849...11S | volume=849 }}</ref>

<ref name=mnras406_3_2000>{{Cite journal | last1=Marks | first1=Michael | last2=Kroupa | first2=Pavel | title=Initial conditions for globular clusters and assembly of the old globular cluster population of the Milky Way | journal=[[Monthly Notices of the Royal Astronomical Society]] | volume=406 | issue=3 | pages=2000–2012 |date=August 2010 | doi=10.1111/j.1365-2966.2010.16813.x | doi-access=free | bibcode=2010MNRAS.406.2000M |arxiv = 1004.2255 | s2cid=118652005 }} Mass is from M<sub>PD</sub> on Table 1.</ref>

<ref name=apj742_1_51>{{Cite journal | display-authors=1 | last1=Boyles | first1=J. | last2=Lorimer | first2=D. R. | last3=Turk | first3=P. J. | last4=Mnatsakanov | first4=R. | last5=Lynch | first5=R. S. | last6=Ransom | first6=S. M. | last7=Freire | first7=P. C. | last8=Belczynski | first8=K. | title=Young Radio Pulsars in Galactic Globular Clusters | journal=The Astrophysical Journal | volume=742 | issue=1 | page=51 |date=November 2011 | doi=10.1088/0004-637X/742/1/51 | bibcode=2011ApJ...742...51B |arxiv = 1108.4402 | s2cid=118649860 }}</ref>

<ref name=mnras385_4_1998>{{Cite journal | display-authors=1 | last1=Koleva | first1=M. | last2=Prugniel | first2=Ph. | last3=Ocvirk | first3=P. | last4=Le Borgne | first4=D. | last5=Soubiran | first5=C. | title=Spectroscopic ages and metallicities of stellar populations: validation of full spectrum fitting | journal=Monthly Notices of the Royal Astronomical Society | volume=385 | issue=4 | pages=1998–2010 |date=April 2008 | doi=10.1111/j.1365-2966.2008.12908.x | doi-access=free | bibcode=2008MNRAS.385.1998K |arxiv = 0801.0871 | s2cid=17571531 }}</ref>

<ref name="Malley">{{cite journal |last1=O'Malley |first1=Erin M. |last2=Gilligan |first2=Christina |last3=Chaboyer |first3=Brian |title=Absolute Ages and Distances of 22 GCs Using Monte Carlo Main-sequence Fitting |journal=The Astrophysical Journal |date=April 2017 |volume=838 |issue=2 |page=162 |doi=10.3847/1538-4357/aa6574 |arxiv=1703.01915 |bibcode=2017ApJ...838..162O |s2cid=11852378 |doi-access=free }}</ref>

<ref name=OMeara1998>{{citation
 | title=Deep-Sky Companions: The Messier Objects
 | first1=Stephen James | last1=O'Meara | first2=David H. | last2=Levy 
 | publisher=Cambridge University Press | postscript=.
 | year=1998 | isbn=978-0521553322 | page=74
 | url=https://books.google.com/books?id=jis4evHuuzUC&pg=PA74 }}</ref>

}}

==External links==
{{Commons category|Messier 15}}
* [http://www.messier.seds.org/m/m015.html Messier 15, SEDS Messier pages]
* [http://gclusters.altervista.org/cluster_4.php?ggc=M+15 Messier 15, Galactic Globular Clusters Database page]
* [http://ukads.nottingham.ac.uk/cgi-bin/nph-bib_query?bibcode=1996AJ....111..267G&amp;db_key=AST Globular Cluster Photometry With the Hubble Space Telescope. V. WFPC Study of M15's Central density Cusp]
* [http://www.wikisky.org/?object=M15&img_source=SDSS Wikisky.org SDSS image of M15]
* {{cite web|last=Gretton|first=Roy|title=M15 – Globular Cluster|url=http://www.deepskyvideos.com/videos/messier/M15_globular_cluster.html|work=Deep Sky Videos|publisher=[[Brady Haran]]|author2=Gray, Meghan}}
* {{WikiSky}}

{{Portal bar|Astronomy|Stars|Outer space}}
{{Catalogs|NGC=7078|M=15}}
{{Messier objects}}
{{Ngc75}}
{{Sky|21|29|58.38||12|10|00.6|33600}}

[[Category:Globular clusters|Messier 015]]
[[Category:Pegasus (constellation)|Messier 015]]
[[Category:Messier objects|015]]
[[Category:NGC objects|Messier 015]]
[[Category:Astronomical X-ray sources]]
[[Category:X-ray astronomy]]
[[Category:Astronomical objects discovered in 1746|17460907]]