View source for Messier 54

{{short description|Globular cluster in Sagittarius}}
{{Infobox globular cluster
| name = [[Messier object|Messier]] 54
| image = [[Image:Messier 54 HST.jpg|300px]]
| caption = M54 by [[Hubble Space Telescope]]; 3.4{{prime}} view
| credit = 
| epoch = [[Epoch (astronomy)#Julian years and J2000|J2000]]
| class = III<ref name=hcob849_11/>
| constellation = [[Sagittarius (constellation)|Sagittarius]]
| ra = {{RA|18|55|03.33}}<ref name=aj140_6_1830/>
| dec = {{DEC|−30|28|47.5}}<ref name=aj140_6_1830/>
| dist_ly = {{Convert|87.4|kly|kpc|abbr=on|lk=on}}<ref name=ramsay_wu_2005/>
| appmag_v = 7.6<ref>{{cite web |url=https://messier.seds.org/m/m054.html |title=Messier 54 |access-date=29 April 2022 |website=SEDS Messier Catalog}}</ref>
| size_v = 12.0{{prime}}
| mass_kg = 
| mass_msol = 
| radius_ly = 153 ly<ref name=trig>From [[trigonometry]]: radius = distance × sin( diameter_angle / 2 ) = 153 ly.</ref>
| v_hb = 
| age = 13 [[Gigayear|Gyr]]<ref name="Geisleretal2007">
{{cite journal
 | last1 = Geisler | first1 = Doug
 | last2 = Wallerstein | first2 = George
 | last3 = Smith | first3 = Verne V.
 | last4 = Casetti-Dinescu | first4 = Dana I.
 | date = 2007
 | title = Chemical Abundances and Kinematics in Globular Clusters and Local Group Dwarf Galaxies and Their Implications for Formation Theories of the Galactic Halo
 | journal = [[Publications of the Astronomical Society of the Pacific]]
 | volume = 119 | issue = 859 | pages = 939–961
 | bibcode = 2007PASP..119..939G
 | doi = 10.1086/521990
|arxiv = 0708.0570 | s2cid = 119599242
 }}</ref>
| notes = Probably extragalactic
| names = M54,<ref name="simbad" /> [[New General Catalogue|NGC]] 6715,<ref name="simbad" /> GCl 104,<ref name="simbad" /> C 1851-305<ref name="simbad" />
}}

'''Messier 54''' (also known as '''M54''' or '''NGC 6715''') is a [[globular cluster]] in the [[constellation]] [[Sagittarius (constellation)|Sagittarius]].{{efn|Specifically in centre this very mildly southern zone of the sky which is well observable from everywhere except the Arctic Circle. However the Sun, considered from our orbit, passes through this zone throughout December. This also makes the cluster mostly risen during day, not night, in the nearest months.}} It was discovered by [[Charles Messier]] in 1778 and then included in [[Messier object|his catalog]] of [[comet]]-like objects. 

It is easily found in the sky, being close to the [[star]] [[Zeta Sagittarii|ζ Sagittarii]]. It is, however, not resolvable into individual stars even with larger amateur [[telescope]]s.

In July 2009, a team of astronomers reported that they had found evidence of an [[intermediate-mass black hole]] in the core of M54.<ref name="Ibata2009">
{{cite journal |last1=Ibata |first1=R. |last2=Bellazzini |first2=M. |last3=Chapman |first3=S. C. |last4=Dalessandro |first4=E. |last5=Ferraro |first5=F. |last6=Irwin |first6=M. |last7=Lanzoni |first7=B. |last8=Lewis |first8=G. F. |last9=Mackey |first9=A. D. |last10=Miocchi |first10=P. |last11=Varghese |first11=A. |display-authors=4 |date=2009 |title=Density and Kinematic Cusps in M54 at the Heart of the Sagittarius Dwarf Galaxy: Evidence for a {{solar mass|10<sup>4</sup>}} Black Hole? |journal=[[Astrophysical Journal Letters]] |volume=699 |issue=2 |page=L169–L173 |arxiv=0906.4894 |bibcode=2009ApJ...699L.169I |doi=10.1088/0004-637X/699/2/L169|s2cid=15976588 }}</ref>

== Distance==
Previously thought to belong to the [[Milky Way]] at a distance from [[Earth]] of about 50,000 [[light-year]]s, it was discovered in 1994 that M54 most likely belongs to the [[Sagittarius Dwarf Elliptical Galaxy]] (SagDEG),<ref name="Siegeletal2007">
{{cite journal
 | last1 = Siegel | first1 = Michael H.
 | display-authors = 4
 | last2 = Dotter | first2 = Aaron
 | last3 = Majewski | first3 = Steven R.
 | last4 = Sarajedini | first4 = Ata
 | last5 = Chaboyer | first5 = Brian
 | last6 = Nidever | first6 = David L.
 | last7 = Anderson | first7 = Jay
 | last8 = Marín-Franch | first8 = Antonio
 | last9 = Rosenberg | first9 = Alfred
 | date = 2007
 | title = The ACS Survey of Galactic Globular Clusters: M54 and Young Populations in the Sagittarius Dwarf Spheroidal Galaxy
 | journal = [[Astrophysical Journal Letters]]
 | volume = 667 | issue = 1 | page = L57–L60
 | bibcode = 2007ApJ...667L..57S
 | doi = 10.1086/522003
|arxiv = 0708.0027 | last10 = Bedin | first10 = Luigi R. | last11 = Aparicio | first11 = Antonio | last12 = King | first12 = Ivan | last13 = Piotto | first13 = Giampaolo | last14 = Reid | first14 = I. Neill | s2cid = 119626792
 }}</ref> making it the first globular cluster formerly thought to be part of our galaxy reassigned to extragalactic status, even if not recognized as such for more than two centuries. As it is located in SagDEG's center, some authors think it actually may be its core;<ref name="Carretta2010">{{cite journal
    | author=Carretta, E.
    | display-authors=4
    | author2=Bragaglia, A.
    | author3=Gratton, R. G.
    | author4=Lucatello, S.
    | author5=Bellazzini, M.
    | author6=Catanzaro, G.
    | author7=Leone, F.
    | author8=Momany, Y.
    | author9=Piotto, G.
    | author10=D'Orazi, V.
    | title=M54 + Sagittarius = ω Centauri
    | journal=The Astrophysical Journal Letters
    | date=2010
    | volume=714
    | issue=1
    | pages=L7–L11
    | bibcode=2010ApJ...714L...7C
    | doi=10.1088/2041-8205/714/1/L7|arxiv = 1002.1963 | s2cid=118440761
 }}</ref> however others have proposed that it is a real globular cluster that fell to the center of this galaxy due to decay of its orbit caused by [[dynamical friction]].<ref name="Bellazzini2008">{{cite journal
    | author=Bellazzini, M.
    | display-authors=4
    | author2=Ibata, R. A.
    | author3=Chapman, S. C.
    | author4=Mackey, A. D.
    | author5=Monaco, L.
    | author6=Irwin, M. J.
    | author7=Martin, N. F.
    | author8=Lewis, G. F.
    | author9=Dalessandro, E.
    | title=The Nucleus of the Sagittarius Dsph Galaxy and M54: a Window on the Process of Galaxy Nucleation
    | journal=The Astronomical Journal
    | date=2008
    | volume=136
    | issue=3
    | pages=1147–1170
    | bibcode=2008AJ....136.1147B
    | doi=10.1088/0004-6256/136/3/1147|arxiv = 0807.0105 | s2cid=53486171
 }}</ref>

Modern estimates now place M54 at a distance of some 87,000 light-years,<ref name=ramsay_wu_2005/> translating into a true radius of 150 light-years across.<ref name=trig/> It is one of the denser of the globulars, being of [[Shapley-Sawyer Concentration Class|class]] III<ref name=hcob849_11/> (I being densest and XII being the least dense). It shines with the [[luminosity]] of roughly 850,000 times that of the [[Sun]] and has an [[absolute magnitude]] of &minus;10.0.[[File:M54map.png|thumbnail|Map showing location of M54]]

==See also==
* [[List of Messier objects]]
* [[Omega Centauri]]
* [[Mayall II]]
* [[Palomar 12]]

==References and footnotes==
{{reflist|2|refs=

<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=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 54 | access-date=2006-11-16 }}</ref>

<ref name=ramsay_wu_2005>{{Cite journal| first1=Gavin | last1=Ramsay | first2=Kinwah | last2=Wu | date=2005 | title=Chandra observations of the globular cluster M54 | arxiv=astro-ph/0510217  | doi=10.1051/0004-6361:20053855 | journal=Astronomy and Astrophysics | volume=447 | issue=1 | pages=199–203 |bibcode = 2006A&A...447..199R | s2cid=18038770 }}</ref>

}}
{{notelist}}
==External links==
{{Commons category|Messier 54}}
* [http://messier.seds.org/m/m054.html M54 @ SEDS Messier pages]
* {{WikiSky}}

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{{DEFAULTSORT:Messier 054}}
[[Category:Globular clusters]]
[[Category:Sagittarius Dwarf Spheroidal Galaxy]]
[[Category:Sagittarius (constellation)]]
[[Category:Messier objects|054]]
[[Category:NGC objects]]
[[Category:Astronomical objects discovered in 1778]]
[[Category:Discoveries by Charles Messier]]