Crater 2 Dwarf

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]

Crater 2
Observation data (J2000.0 epoch)
ConstellationCrater[1]
Right ascension11h 49m 14.400s
177.310°±0.03°[1]
Declination−18° 24′ 46.80″
−18.413°±0.03°[1]
Heliocentric radial velocity88 km/s[2]
Galactocentric velocity-74 km/s[2]
Distance383,000 ly (117.5 kpc)[1]
Apparent magnitude (V)12.15 mag[1]
Absolute magnitude (V)−8.2±0.1 mag[1]
Characteristics
TypedSph[1]
Apparent size (V)62.4′ (rh=31.2′ ± 2.5′)[1]
6,950 ly (2,132 pc)
rh=1066pc ± 84pc[1]
Notable features4th 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]

See also

References
  1. Torrealba, 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.
  2. Kashibadze, Olga G.; Karachentsev, Igor D. (2018). "Cosmic flow around local massive galaxies". Astronomy & Astrophysics. 609: A11. arXiv:1709.09420. Bibcode:2018A&A...609A..11K. doi:10.1051/0004-6361/201731645. S2CID 55486336.
  3. Croswell, Ken (14 April 2016). "Never-before-seen galaxy spotted orbiting the Milky Way". New Scientist. Retrieved 14 April 2016.
  4. Howard, Jacqueline (2016-04-16). "Elusive Dwarf Galaxy Found Orbiting Our Milky Way". Huffington Post. Retrieved 2016-04-19.
  5. Ji, Alexander P.; Koposov, Sergey E.; Li, Ting S.; Erkal, Denis; Pace, Andrew B.; Simon, Joshua D.; Belokurov, Vasily; Cullinane, Lara R.; Da Costa, Gary S.; Kuehn, Kyler; Lewis, Geraint F.; MacKey, Dougal; Shipp, Nora; Simpson, Jeffrey D.; Zucker, Daniel B.; Hansen, Terese T.; Bland-Hawthorn, Joss; S5 Collaboration (2021). "Kinematics of Antlia 2 and Crater 2 from the Southern Stellar Stream Spectroscopic Survey (S 5)". The Astrophysical Journal. 921 (1): 32. arXiv:2106.12656. Bibcode:2021ApJ...921...32J. doi:10.3847/1538-4357/ac1869. S2CID 235624056.
  6. Borukhovetskaya, 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.
  7. McGaugh, Stacy S. (2016-11-14). "MOND Prediction for the Velocity Dispersion of the 'Feeble Giant' Crater II". The Astrophysical Journal. 832 (1): L8. arXiv:1610.06189. Bibcode:2016ApJ...832L...8M. doi:10.3847/2041-8205/832/1/L8. ISSN 2041-8213. S2CID 51764960.
  8. Caldwell, Nelson; Walker, Matthew G.; Mateo, Mario; Olszewski, Edward W.; Koposov, Sergey; Belokurov, Vasily; Torrealba, Gabriel; Geringer-Sameth, Alex; Johnson, Christian I. (2017-04-10). "Crater 2: An Extremely Cold Dark Matter Halo". The Astrophysical Journal. 839 (1): 20. arXiv:1612.06398. Bibcode:2017ApJ...839...20C. doi:10.3847/1538-4357/aa688e. hdl:10150/623952. ISSN 1538-4357. S2CID 119422981.


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