Crater 2 Dwarf
Dwarf satellite galaxy of the Milky Way
From Wikipedia, the free encyclopedia
Crater 2 is a low-surface-brightness dwarf satellite galaxy of the Milky Way,[1] located approximately 380,000 ly from Earth. Its discovery in 2016 revealed significant gaps in astronomers' understanding of galaxies possessing relatively small half-light diameters and suggested the possibility of many undiscovered dwarf galaxies orbiting the Milky Way.[3] Crater 2 was identified in imaging data from the VST ATLAS survey.[3]
177.310°±0.03°[1]
−18.413°±0.03°[1]
| Crater 2 | |
|---|---|
| Observation data (J2000.0 epoch) | |
| Constellation | Crater[1] |
| Right ascension | 11h 49m 14.400s 177.310°±0.03°[1] |
| Declination | −18° 24′ 46.80″ −18.413°±0.03°[1] |
| Heliocentric radial velocity | 88 km/s[2] |
| Galactocentric velocity | -74 km/s[2] |
| Distance | 383,000 ly (117.5 kpc)[1] |
| Apparent magnitude (V) | 12.15 mag[1] |
| Absolute magnitude (V) | −8.2±0.1 mag[1] |
| Characteristics | |
| Type | dSph[1] |
| Apparent size (V) | 62.4′ (rh=31.2′ ± 2.5′)[1] 6,950 ly (2,132 pc) rh=1066pc ± 84pc[1] |
| Notable features | 4th largest satellite galaxy to Milky Way[1] |
The galaxy has a half-light radius of ~1100 pc, making it the fourth largest satellite of the Milky Way.[1] It has an angular size about double of that of the moon.[3][4] Despite the large size, Crater 2 has a surprisingly low surface brightness, implying that it is not very massive.[5] In addition, its velocity dispersion is also low, suggesting it may have formed in a halo of low dark matter density.[6] Alternatively, it may be a result of tidal interactions with it and larger galaxies, such as the Milky Way and the Large Magellanic Cloud,[5] but according to some simulations, this would not explain the relatively large size.[6] This unusually low velocity dispersion was predicted using Modified Newtonian Dynamics, an alternative to the dark matter hypothesis.[7] This prediction was later confirmed by observations.[8]
