Editing Messier 54 (section)

== 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]]