globular cluster From Wikipedia, the free encyclopedia
Messier 54 (or M54 or NGC 6715) is a globular cluster in the constellation Sagittarius. It was discovered by Charles Messier in 1778. Later, he included it in his catalog of comet-like objects.
M54 was thought to belong to our Milky Way galaxy, but in 1994 it was discovered that M54 belongs to the Sagittarius dwarf elliptical galaxy ('Sag DEG').[1]
M54 is some 87,000 light-years from us, and has a radius of 150 light-years across. It is one of the most dense globulars. 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 in the sky, being close to the star ζ Sagittarii. Individual stars cannot be seen with amateur telescopes.
It is on or near SagDEG's center. Some authors think it actually may be its core;[2] but others do not.[3]
In July 2009, a team of astronomers found evidence of a medium-sized black hole in the core of M54.[4]
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