Messier Index/M54
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Messier 54 (also known as M54 or NGC 6715) is a w:globular cluster in the w:constellation Sagittarius. It was discovered by w:Charles Messier in w:1778 and subsequently included in his catalog of w:comet-like objects.
Previously thought to be at a distance from w:Earth of about 50,000 w:light-years, it was discovered in w:1994 that M54 was most likely not part of the w:Milky Way, but actually part of the w:Sagittarius Dwarf Elliptical Galaxy, (SagDEG),[1] 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 denser of the globulars, being of class III (I being densest and XII being the least dense). It shines with the w:luminosity of roughly 850,000 times that of the w:Sun and has an w:absolute magnitude of -10.0.
M54 is easily found on the sky, being close to the w:star ζ Sagittarii. It is however, not resolvable into individual stars even with larger amateur w:telescopes.
In July of 2009, a team of astronomers reported that they had found evidence of an w:intermediate-mass black hole in the core of M54.[2] This was the first report of such a black hole in any globular cluster.