Messier 54

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.

Messier 54
M54 by Hubble Space Telescope; 3.4′ view
Credit: ESA/Hubble & NASA
Observation data (J2000 epoch)
ClassIII[1]
ConstellationSagittarius
Right ascension 18h 55m 03.33s[2]
Declination−30° 28′ 47.5″[2]
Distance87.4 kly (26.8 kpc)[3]
Apparent magnitude (V)8.37[4]
Apparent dimensions (V)12′.0
Physical characteristics
Radius153 ly[5]
Estimated age13 Gyr[6]
Notable featuresProbably extragalactic
Other designationsM54,[4] NGC 6715,[4] GCl 104,[4] C 1851-305[4]

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.

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),[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. 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]

Modern estimates now place M54 at a distance of some 87,000 light-years,[3] translating into a true radius of 150 light-years across.[5] It is one of the denser of the globulars, being of class III[1] (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.

Intermediate-mass black hole

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. Bibcode:1927BHarO.849...11S.
  2. 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. arXiv:1008.2755. Bibcode:2010AJ....140.1830G. doi:10.1088/0004-6256/140/6/1830.
  3. Ramsay, Gavin; Wu, Kinwah (2005). "Chandra observations of the globular cluster M54". Astronomy and Astrophysics. 447: 199–203. arXiv:astro-ph/0510217. Bibcode:2006A&A...447..199R. doi:10.1051/0004-6361:20053855.
  4. "M 54". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-11-16.
  5. From trigonometry: radius = distance × sin( diameter_angle / 2 ) = 153 ly.
  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". Publications of the Astronomical Society of the Pacific. 119 (859): 939–961. arXiv:0708.0570. Bibcode:2007PASP..119..939G. doi:10.1086/521990.
  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". Astrophysical Journal Letters. 667 (1): L57–L60. arXiv:0708.0027. Bibcode:2007ApJ...667L..57S. doi:10.1086/522003.
  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. arXiv:1002.1963. Bibcode:2010ApJ...714L...7C. doi:10.1088/2041-8205/714/1/L7.
  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. arXiv:0807.0105. Bibcode:2008AJ....136.1147B. doi:10.1088/0004-6256/136/3/1147.
  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?". Astrophysical Journal Letters. 699 (2): L169–L173. arXiv:0906.4894. Bibcode:2009ApJ...699L.169I. doi:10.1088/0004-637X/699/2/L169.

This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.