NGC 2808

NGC 2808 is a globular cluster[6] in the constellation Carina. The cluster belongs to the Milky Way, and is one of our home galaxy's most massive clusters, containing more than a million stars. It is estimated to be 12.5-billion years old.

NGC 2808
A Hubble Space Telescope (HST) image of NGC 2808.
Credit: HST/NASA/ESA.
Observation data (J2000 epoch)
ClassI[1]
ConstellationCarina
Right ascension09h 12m 03.10s[2]
Declination–64° 51′ 48.6″[2]
Distance31.3 kly (9.6 kpc)[3]
Apparent magnitude (V)6.2[4]
Apparent dimensions (V)13′.8[4]
Physical characteristics
Mass1.42×106[3] M☉
Metallicity = –1.14[3] dex
Estimated age10.2 Gyr[5]
Other designationsGCl 13, Melotte 95[6]

Star Generations

It had been thought that NGC 2808, like typical globular clusters, contains only one generation of stars formed simultaneously from the same material. In 2007, a team of astronomers led by Giampaolo Piotto of the University of Padua in Italy investigated Hubble Space Telescope images of NGC 2808 taken in 2005 and 2006 with Hubble's Advanced Camera for Surveys. Unexpectedly, they found that this cluster is composed of three generations of stars, all born within 200 million years of the formation of the cluster.[7]

Astronomers have argued that globular clusters can produce only one generation of stars, because the radiation from first generation stars would drive the residual gas not consumed in the first star generation phase out of the cluster. However, the great mass of a cluster such as NGC 2808 may suffice to gravitationally counteract the loss of gaseous matter. Thus, a second and a third generation of stars may form.

An alternative explanation for the three star generations of NGC 2808 is that it may actually be the remnant of a dwarf galaxy that collided with the Milky Way, the Sausage Galaxy.[8]

See also

References
  1. Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin, 849 (849): 11–14, Bibcode:1927BHarO.849...11S
  2. Goldsbury, Ryan; et al. (December 2010), "The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters", The Astronomical Journal, 140 (6): 1830–1837, arXiv:1008.2755, Bibcode:2010AJ....140.1830G, doi:10.1088/0004-6256/140/6/1830.
  3. Boyles, J.; et al. (November 2011), "Young Radio Pulsars in Galactic Globular Clusters", The Astrophysical Journal, 742 (1): 51, arXiv:1108.4402, Bibcode:2011ApJ...742...51B, doi:10.1088/0004-637X/742/1/51
  4. "Data for NGC 2808". NGC/IC Project. Archived from the original on 18 December 2012. Retrieved 19 November 2013.
  5. Koleva, M.; et al. (April 2008), "Spectroscopic ages and metallicities of stellar populations: validation of full spectrum fitting", Monthly Notices of the Royal Astronomical Society, 385 (4): 1998–2010, arXiv:0801.0871, Bibcode:2008MNRAS.385.1998K, doi:10.1111/j.1365-2966.2008.12908.x
  6. "NGC 2808". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2007-05-07.
  7. Piotto, G.; et al. (May 2007). "A Triple Main Sequence in the Globular Cluster NGC 2808". The Astrophysical Journal. 661 (1): L53–L56. arXiv:astro-ph/0703767. Bibcode:2007ApJ...661L..53P. doi:10.1086/518503.
  8. C., Myeong, G.; W., Evans, N.; V., Belokurov; L., Sanders, J.; E., Koposov, S. (2018). "The Sausage Globular Clusters". Bibcode:2018arXiv180500453M. Cite journal requires |journal= (help)
  • Media related to NGC 2808 at Wikimedia Commons


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