Messier 54

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Messier 54

Greyscale image created from the HST's Advanced Camera for Surveys.
Observation data (J2000 epoch)
Class III
Constellation Sagittarius
Right ascension 18h 55m 03.28s[1]
Declination -30° 28′ 42.6″[1]
Distance 87.4 kly[2] (26.8 kpc)
Apparent magnitude (V) 8.37[1]
Apparent dimensions (V) 12′.0
Physical characteristics
Mass kg ( M{\odot})
Radius 153 ly[3]
Estimated age 13 Gyr[4]
Notable features Probably extragalactic
Other designations M54,[1] NGC 6715,[1] GCl 104[1]
See also: Globular cluster, List of globular clusters
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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 be at a distance from Earth of about 50,000 light-years, it was discovered in 1994 that M54 was most likely not part of the Milky Way, but actually part of the Sagittarius Dwarf Elliptical Galaxy, (SagDEG),[5] making it the first extragalactic globular cluster ever discovered, even if it wasn't 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 more dense 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.

M54 is easily found on the sky, being close to the star ζ Sagittarii. It is however, not resolvable into individual stars even with larger amateur telescopes.

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  1. ^ a b c d e f SIMBAD Astronomical Database. Results for NGC 6715. Retrieved on 2006-11-16.
  2. ^ Gavin Ramsay and Kinwah Wu, Chandra observations of the globular cluster M54
  3. ^ distance × sin( diameter_angle / 2 ) = 153 ly. radius
  4. ^ Geisler, Doug; Wallerstein, George; Smith, Verne V. & Casetti-Dinescu, Dana I. (September 2007), “Chemical Abundances and Kinematics in Globular Clusters and Local Group Dwarf Galaxies and Their Implications for Formation Theories of the Galactic Halo”, The Publications of the Astronomical Society of the Pacific 119 (859): 939-961, <http://adsabs.harvard.edu/abs/2007PASP..119..939G> 
  5. ^ Siegel, Michael H.; Dotter, Aaron; Majewski, Steven R.; Sarajedini, Ata; Chaboyer, Brian; Nidever, David L.; Anderson, Jay; Marín-Franch, Antonio; et al. (September 2007), “The ACS Survey of Galactic Globular Clusters: M54 and Young Populations in the Sagittarius Dwarf Spheroidal Galaxy”, The Astrophysical Journal 667 (1): L57-L60, <http://adsabs.harvard.edu/cgi-bin/bib_query?bibcode=2007ApJ...667L..57S>