Messier 54
{{short description|Globular cluster in Sagittarius}}
{{Infobox globular cluster
| name = Messier 54
| image = 300px
| caption = M54 by Hubble Space Telescope; 3.4{{prime}} view
| credit =
| epoch = J2000
| constellation = Sagittarius
| dist_ly = {{Convert|87.4|kly|kpc|abbr=on|lk=on}}
| appmag_v = 7.6{{cite web |url=https://messier.seds.org/m/m054.html |title=Messier 54 |access-date=29 April 2022 |website=SEDS Messier Catalog}}
| size_v = 12.0{{prime}}
| mass_kg =
| mass_msol =
| radius_ly = 153 lyFrom trigonometry: radius = distance × sin( diameter_angle / 2 ) = 153 ly.
| v_hb =
| age = 13 Gyr
{{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
}}
| notes = Probably extragalactic
| names = M54, NGC 6715, GCl 104, C 1851-305
}}
Messier 54 (also known as M54 or NGC 6715) is a globular cluster in the 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 his catalog of objects that could be mistaken for comets.
It is easily found in the sky, being close to the star ζ Sagittarii. It is, however, not resolvable into individual stars even with larger amateur telescopes.
In July 2009, a team of astronomers reported that they had found evidence of an intermediate-mass black hole in the core of M54.
{{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|104}} 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 }}
Distance
Previously thought to belong to the Milky Way at a distance from Earth of about 50,000 light-years, it was discovered in 1994 that M54 most likely belongs to the Sagittarius Dwarf Elliptical Galaxy (SagDEG),
{{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
}} 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;{{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
}} 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.{{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
}}
Modern estimates now place M54 at a distance of some 87,000 light-years, translating into a true radius of 150 light-years across. It is one of the denser of the globulars, being of class III (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 −10.0.File:M54map.png
See also
References and footnotes
External links
{{Commons category|Messier 54}}
- [http://messier.seds.org/m/m054.html M54 @ SEDS Messier pages]
- {{WikiSky}}
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{{Messier objects}}
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{{catalogs|M=54|NGC=6715}}
{{Ngc70}}
{{Sky|18|55|03.28|-|30|28|42.6|87400}}
{{DEFAULTSORT:Messier 054}}
Category:Sagittarius Dwarf Spheroidal Galaxy
Category:Sagittarius (constellation)