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) | |
| 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]
See also
editReferences
edit- ^ a b c d e f g h i j k l 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.
- ^ a b 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.
- ^ a b c Croswell, Ken (14 April 2016). "Never-before-seen galaxy spotted orbiting the Milky Way". New Scientist. Retrieved 14 April 2016.
- ^ Howard, Jacqueline (2016-04-16). "Elusive Dwarf Galaxy Found Orbiting Our Milky Way". Huffington Post. Retrieved 2016-04-19.
- ^ a b 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.
{{cite journal}}: CS1 maint: numeric names: authors list (link) - ^ a b 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.
- ^ 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.
- ^ 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.
