NGC 2808 is a globular cluster[6] in the constellationCarina. The cluster currently belongs to the Milky Way, although it was likely stolen from a dwarf galaxy that collided with the Milky Way. NGC 2808 is one of the Milky Way's most massive clusters, containing more than a million stars. It is estimated to be 12.5 billion years old.
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.[8]
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 core of a dwarf galaxy that collided with the Milky Way, called the Sausage Galaxy.[9]
^Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin, 849 (849): 11–14, Bibcode:1927BHarO.849...11S
^Carballo-Bello, Julio A.; Martínez-Delgado, David; Navarrete, Camila; Catelan, Márcio; Muñoz, Ricardo R.; Antoja, Teresa; Sollima, Antonio (2017), "Tails and streams around the Galactic globular clusters NGC 1851, NGC 1904, NGC 2298 and NGC 2808", Monthly Notices of the Royal Astronomical Society, 474: 683–695, arXiv:1710.08927, doi:10.1093/mnras/stx2767
Media related to NGC 2808 at Wikimedia Commons
