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Crater 2 Dwarf
Dwarf satellite galaxy of the Milky Way
Coordinates: 11h 49m 14.4s, −18° 24′ 46.8″

Crater 2 is a low-surface-brightness dwarf satellite galaxy of the Milky Way, 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. Crater 2 was identified in imaging data from the VST ATLAS survey.

The galaxy has a half-light radius of ~1100 pc, making it the fourth largest satellite of the Milky Way. It has an angular size about double of that of the moon. Despite the large size, Crater 2 has a surprisingly low surface brightness, implying that it is not very massive. In addition, its velocity dispersion is also low, suggesting it may have formed in a halo of low dark matter density. Alternatively, it may be a result of tidal interactions with it and larger galaxies, such as the Milky Way and the Large Magellanic Cloud, but according to some simulations, this would not explain the relatively large size. This unusually low velocity dispersion was predicted using Modified Newtonian Dynamics, an alternative to the dark matter hypothesis. This prediction was later confirmed by observations.

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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. https://doi.org/10.1093%2Fmnras%2Fstw733 ↩

  2. Croswell, Ken (14 April 2016). "Never-before-seen galaxy spotted orbiting the Milky Way". New Scientist. Retrieved 14 April 2016. /wiki/Ken_Croswell ↩

  3. Croswell, Ken (14 April 2016). "Never-before-seen galaxy spotted orbiting the Milky Way". New Scientist. Retrieved 14 April 2016. /wiki/Ken_Croswell ↩

  4. 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. https://doi.org/10.1093%2Fmnras%2Fstw733 ↩

  5. Croswell, Ken (14 April 2016). "Never-before-seen galaxy spotted orbiting the Milky Way". New Scientist. Retrieved 14 April 2016. /wiki/Ken_Croswell ↩

  6. Howard, Jacqueline (2016-04-16). "Elusive Dwarf Galaxy Found Orbiting Our Milky Way". Huffington Post. Retrieved 2016-04-19. http://www.huffingtonpost.com/entry/dwarf-galaxy-crater-2_us_57110c70e4b06f35cb6f5d5f ↩

  7. 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) https://doi.org/10.3847%2F1538-4357%2Fac1869 ↩

  8. 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. https://doi.org/10.1093%2Fmnras%2Fstac653 ↩

  9. 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) https://doi.org/10.3847%2F1538-4357%2Fac1869 ↩

  10. 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. https://doi.org/10.1093%2Fmnras%2Fstac653 ↩

  11. 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. https://doi.org/10.3847%2F2041-8205%2F832%2F1%2FL8 ↩

  12. 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. https://doi.org/10.3847%2F1538-4357%2Faa688e ↩