| M60-UCD1 | |
|---|---|
 A picture of M60-UCD1 taken by theHubble Space Telescope | |
| Observation data (J2000.0epoch) | |
| Constellation | Virgo |
| Right ascension | 12h 43m 35.976s[1] |
| Declination | 11° 32m 4.92s[1] |
| Redshift | 0.004263±0.0[2] |
| Heliocentric radial velocity | 1,278±0 km/s[2] |
| Galactocentric velocity | 1,229±2 km/s[2] |
| Distance | 48.60 ± 3.262 Mly (14.9 ± 1.0 Mpc)h−1 0.6774 (Comoving)[2] |
| Group orcluster | M60 Group |
| Apparent magnitude (V) | 14.2[1] |
| Characteristics | |
| Mass | (2.0±0.3)×108 (dynamical mass)[1] M☉ |
| Size | 158 ± 3.26 ly (48.4 ± 1.0 pc) (Half-light diameter)[1] |
| Half-light radius (physical) | 78.9 ± 1.63 ly (24.2 ± 0.5 pc)[1] |
| Other designations | |
| M60-UCD1,SDSS J124335.96+113204.6[3] | |
References:[3] | |
M60-UCD1 is anultracompact dwarf galaxy. It is 49 millionlight years from Earth, close toMessier 60 (M60,NGC 4649) in theVirgo Cluster. Half of its stellar mass is in the central sphere 160 light years in diameter.[4]
M60-UCD1's dynamical mass is200±30 millionsolar masses (M☉).[1] Colours and lack of colour gradients indicate a uniform stellar population about14.5±0.5 billion years old(indistinguishable from the age of theUniverse).[1][6] Theirmetallicity is similar to that of theSun. The orbital velocity dispersion of the innermost stars exceeds 100 km/s,[6] due to the gravity of a dense mass concentration. The galactic nucleus contains a bright and variableX-ray source,[1] presumably asupermassive black hole with a mass of 20 million M☉ (10% of the dynamical mass of the entire galaxy).[7] With this proportion of the mass of the black hole to that of the whole galaxy, it is one of the most black hole dominated galaxies known.[8]
M60-UCD1 is believed to be the stripped core of a much more massive galaxy, whose mass was stripped in an encounter with M60 some 10 billion years ago. It may yet be absorbed completely by M60, its central black hole merging with M60's as well. The galaxy may have once had some 10 billion stars.[8]
As of 2013, it is possibly the densest knowngalaxy with over one hundred stars per cubic light-year.[9] As of 2014, it is the smallest and least massive galaxy known to host acentral black hole. It was previously known as the most massive ultracompact dwarf galaxy known.[8]
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