M60-UCD1 is an ultracompact dwarf galaxy and possibly the densest known galaxy. It is 54 million light years from Earth, close to Messier 60 (NGC 4649). Half of its mass is in the central sphere 160 light years in diameter. Its mass is 200 million solar masses. Metalicity is similar to the sun. There is a bright X-ray source in the centre, possibly a black hole.
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- ^ "Astronomers Discover Densest Galaxy Ever". ScienceDaily. Retrieved 26 September 2013.
- ^ "M60-UCD1: An Ultra-Compact Dwarf Galaxy". NASA. Retrieved 25 September 2013.
- Strader, Jay; Seth, Anil C.; Forbes, Duncan A.; Fabbiano, Giuseppina; Romanowsky, Aaron J.; Brodie, Jean P.; Conroy, Charlie; Caldwell, Nelson; Pota, Vincenzo; Usher, Christopher; Arnold, Jacob A.; "The Densest Galaxy", The Astrophysical Journal Letters, Volume 775, Issue 1, article id. L6, 6 pp., September 2013; doi:10.1088/2041-8205/775/1/L6 ; Bibcode: 2013ApJ...775L...6S ; arXiv:1307.7707