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Messier 54

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Title: Messier 54  
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Subject: Sagittarius Dwarf Spheroidal Galaxy, Globular cluster, Sagittarius (constellation), Ring Nebula, List of Messier objects
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Messier 54

Messier 54
M54 by Hubble Space Telescope; 3.4′ view
Credit: ESA/Hubble & NASA
Observation data (J2000 epoch)
Class III[1]
Constellation Sagittarius
Right ascension 18h 55m 03.33s[2]
Declination −30° 28′ 47.5″[2]
Distance 87.4 kly (26.8 kpc)[3]
Apparent magnitude (V) 8.37[4]
Apparent dimensions (V) 12′.0
Physical characteristics
Radius 153 ly[5]
Estimated age 13 Gyr[6]
Notable features Probably extragalactic
Other designations M54,[4] NGC 6715,[4] GCl 104,[4] C 1851-305[4]

Messier 54 (also known as M54 or NGC 6715) is a globular cluster in the constellation Sagittarius. It was discovered by Charles Messier in 1778 and subsequently included in his catalog of comet-like objects.

Previously thought to belong to our galaxy 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),[7] 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 nearly two and a quarter centuries.

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 Shapley-Sawyer Concentration 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.

As it is located on SagDEG's center, some authors think it actually may be its core;[8] 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.[9]

M54 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.[10]

Map showing location of M54 (RobertoMura)

See also

References

  1. ^ Shapley, Harlow; Sawyer, Helen B. (August 1927). "A Classification of Globular Clusters". Harvard College Observatory Bulletin 849 (849): 11–14.  
  2. ^ a b Goldsbury, Ryan; et al. (December 2010). "The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters". The Astronomical Journal 140 (6): 1830–1837.  
  3. ^ Ramsay, Gavin; Wu, Kinwah (2005). "Chandra observations of the globular cluster M54". Astronomy and Astrophysics 447: 199.  
  4. ^ a b c d e "SIMBAD Astronomical Objects Database". Results for NGC 6715. Retrieved 2006-11-16. 
  5. ^ distance × sin( diameter_angle / 2 ) = 153 ly. radius
  6. ^ Geisler, Doug; Wallerstein, George; Smith, Verne V.; Casetti-Dinescu, Dana I. (2007). "Chemical Abundances and Kinematics in Globular Clusters and Local Group Dwarf Galaxies and Their Implications for Formation Theories of the Galactic Halo".  
  7. ^ Siegel, Michael H.; Dotter, Aaron; Majewski, Steven R.; Sarajedini, Ata; et al. (2007). "The ACS Survey of Galactic Globular Clusters: M54 and Young Populations in the Sagittarius Dwarf Spheroidal Galaxy".  
  8. ^ Carretta, E.; Bragaglia, A.; Gratton, R. G.; Lucatello, S.; et al. (2010). "M54 + Sagittarius = ω Centauri". The Astrophysical Journal Letters 714 (1): L7–L11.  
  9. ^ Bellazzini, M.; Ibata, R. A.; Chapman, S. C.; Mackey, A. D.; et al. (2008). "The Nucleus of the Sagittarius Dsph Galaxy and M54: a Window on the Process of Galaxy Nucleation". The Astronomical Journal 136 (3): 1147–1170.  
  10. ^ Ibata, R.; Bellazzini, M.; Chapman, S. C.; Dalessandro, E.; et al. (2009). "Density and Kinematic Cusps in M54 at the Heart of the Sagittarius Dwarf Galaxy: Evidence for a 104 M Black Hole?".  

External links

  • M54 @ SEDS Messier pages
  • Messier 54 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images

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