NGC 2808

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NGC 2808
NGC 2808 HST.jpg
A Hubble Space Telescope (HST) image of NGC 2808.
Observation data (J2000 epoch)
Class I[1]
Constellation Carina
Right ascension 09h 12m 03.10s[2]
Declination –64° 51′ 48.6″[2]
Distance 31.3 kly (9.6 kpc)[3]
Apparent magnitude (V) 6.2[4]
Apparent dimensions (V) 13′.8[4]
Physical characteristics
Mass 1.42×106[3] M
Metallicity  = –1.14[3] dex
Estimated age 10.2 Gyr[5]
Other designations GCl 13[6]
See also: Globular cluster, List of globular clusters

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.

Star Generations[edit]

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[edit]


  1. ^ Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin (849): 11–14, Bibcode:1927BHarO.849...11S 
  2. ^ a b 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:1008.2755Freely accessible, Bibcode:2010AJ....140.1830G, doi:10.1088/0004-6256/140/6/1830. 
  3. ^ a b c Boyles, J.; et al. (November 2011), "Young Radio Pulsars in Galactic Globular Clusters", The Astrophysical Journal, 742 (1): 51, arXiv:1108.4402Freely accessible, Bibcode:2011ApJ...742...51B, doi:10.1088/0004-637X/742/1/51 
  4. ^ a b "Data for NGC 2808". NGC/IC Project. 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:0801.0871Freely accessible, Bibcode:2008MNRAS.385.1998K, doi:10.1111/j.1365-2966.2008.12908.x 
  6. ^ a b "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/0703767Freely accessible. 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".