NGC 2808 is a
globular cluster in the
constellation
A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object.
The origins of the e ...
Carina. The cluster belongs to the
Milky Way, and is one of our home
galaxy
A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. ...
's most massive clusters, containing more than a million stars. It is estimated to be 12.5-billion years old.
The cluster is being disrupted by the
galactic tide, trailing a long
tidal tail.
Star generations
It had been thought that NGC 2808, like typical
globular clusters, contains only one generation of
star
A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
s 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.
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, the
Sausage Galaxy.
See also
*
Messier 54 and
Messier 79, two other extragalactic globular clusters
*
Omega Centauri
References
External links
*
{{DEFAULTSORT:NGC 2808
Globular clusters
Carina (constellation)
2808
Canis Major Overdensity