This Hubble telescope image of a dense swarm of stars shows the central region of the globular cluster NGC 2808.
Astronomers were surprised when Hubble spied three generations of cluster stars. The discovery is far different from the standard picture of a globular cluster. For decades, astronomers thought that cluster stars formed at the same time, in the same place, and from the same material, and have co-evolved for billions of years.
Globular clusters are the homesteaders of our Milky Way Galaxy, born during our galaxy's formation. They are compact swarms of typically hundreds of thousands of stars held together by gravity.
All the stars in NGC 2808 were born within 200 million years very early in the life of the 12.5-billion-year-old massive cluster. Of the about 150 known globular clusters in our Milky Way Galaxy, NGC 2808 is one of the most massive, containing more than 1 million stars.
The sharp resolution of Hubble's Advanced Camera for Surveys measured the brightness and colors of the cluster stars to find the three stellar populations.
The Hubble images were taken in May 2005 and in August and November 2006.
The science team includes G. Piotto, A.P. Milone, and S. Villanova (University of Padua [Padova]), L.R. Bedin (European Space Agency, European Organization for Astronomical Research in the Southern Hemisphere, and Space Telescope Science Institute), J. Anderson (Rice University), I.R. King (University of Washington), S. Cassisi and A. Pietrinferni (INAF- Astronomical Observatory of Collurania, Teramo), and A. Renzini (INAF-Astronomical Observatory of Padua [Padova]).