Crater 2 is a
low-surface-brightnessdwarfsatellite 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]
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]
^
abcdefghijklTorrealba, G.; Koposov, S. E.; Belokurov, V.; Irwin, M. (2016). "The feeble giant. Discovery of a large and diffuse Milky Way dwarf galaxy in the constellation of Crater". Monthly Notices of the Royal Astronomical Society. 459 (3): 2370–2378.
arXiv:1601.07178.
Bibcode:
2016MNRAS.459.2370T.
doi:
10.1093/mnras/stw733.
^
abBorukhovetskaya, Alexandra; Navarro, Julio F.; Errani, Raphaël; Fattahi, Azadeh (2022). "Galactic tides and the Crater II dwarf spheroidal: A challenge to LCDM?". Monthly Notices of the Royal Astronomical Society. 512 (4): 5247–5257.
arXiv:2112.01540.
Bibcode:
2022MNRAS.512.5247B.
doi:
10.1093/mnras/stac653.