Astronomy:Crater 2 Dwarf

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Short description: Dwarf satellite galaxy of the Milky Way

Coordinates: Sky map 11h 49m 14.4s, −18° 24′ 46.8″

Crater 2
Observation data (J2000.0 epoch)
ConstellationCrater[1]
Right ascension 11h 49m 14.400s
177.310°±0.03°[1]
Declination−18° 24′ 46.80″
−18.413°±0.03°[1]
Helio 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]

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]

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. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 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. doi:10.1093/mnras/stw733. Bibcode: 2016MNRAS.459.2370T. 
  2. ↑ 2.0 2.1 Kashibadze, Olga G.; Karachentsev, Igor D. (2018). "Cosmic flow around local massive galaxies". Astronomy & Astrophysics 609: A11. doi:10.1051/0004-6361/201731645. Bibcode: 2018A&A...609A..11K. 
  3. ↑ 3.0 3.1 3.2 Croswell, Ken (14 April 2016). "Never-before-seen galaxy spotted orbiting the Milky Way". New Scientist. https://www.newscientist.com/article/2084438-never-before-seen-galaxy-spotted-orbiting-the-milky-way/. 
  4. ↑ Howard, Jacqueline (2016-04-16). "Elusive Dwarf Galaxy Found Orbiting Our Milky Way". Huffington Post. http://www.huffingtonpost.com/entry/dwarf-galaxy-crater-2_us_57110c70e4b06f35cb6f5d5f. 
  5. ↑ 5.0 5.1 Ji, Alexander P.; Koposov, Sergey E.; Li, Ting S.; Erkal, Denis; Pace, Andrew B.; Simon, Joshua D.; Belokurov, Vasily; Cullinane, Lara R. et al. (2021). "Kinematics of Antlia 2 and Crater 2 from the Southern Stellar Stream Spectroscopic Survey (S 5)". The Astrophysical Journal 921 (1): 32. doi:10.3847/1538-4357/ac1869. Bibcode: 2021ApJ...921...32J. 
  6. ↑ 6.0 6.1 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. doi:10.1093/mnras/stac653. Bibcode: 2022MNRAS.512.5247B. 
  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. doi:10.3847/2041-8205/832/1/L8. ISSN 2041-8213. Bibcode: 2016ApJ...832L...8M. 
  8. ↑ Caldwell, Nelson; Walker, Matthew G.; Mateo, Mario; Olszewski, Edward W.; Koposov, Sergey; Belokurov, Vasily; Torrealba, Gabriel; Geringer-Sameth, Alex et al. (2017-04-10). "Crater 2: An Extremely Cold Dark Matter Halo". The Astrophysical Journal 839 (1): 20. doi:10.3847/1538-4357/aa688e. ISSN 1538-4357. Bibcode: 2017ApJ...839...20C. 

External links




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