Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003msngr.112...31g&link_type=abstract
The Messenger (ISSN 0722-6691), No. 112, p. 31 - 36 (June 2003)
Astronomy and Astrophysics
Astrophysics
Globular Clusters, Dwarfs, Abundances
Scientific paper
Globular Clusters are huge, very compact aggregates of hundreds of thousands of stars (see Figure 1). There are about 150 such systems in our Galaxy, the closest being about 10,000 light years from us; some of them are visible with the naked eye (ω Centauri, 47 Tucanae), and many others are spectacular objects visible with small telescopes. Globular Clusters play an important role in modern astrophysics mainly because they are the oldest objects in our Galaxy and in the whole Universe that we can accurately date. Provided that their distances are known, ages of Globular Clusters can in fact be determined quite precisely from the luminosity of the turn-off stars, that is the stars that are exhausting Hydrogen at their centre. The oldest Globular Clusters are so old that they formed when the Universe was very young, and very different from what it appears now. Accurately dating them is then basic to constraining the early epochs of formation of our own Galaxy, and even the age of the Universe. This last is important for cosmology: combined with estimates of the Hubble constant, it may tell us about the presence and nature of the mysterious dark energy, whose presence is suggested by the apparent decline of the luminosity of type Ia supernovae at high redshifts (Perlmutter et al. 1999), and by the characteristics of the X-ray emission of galaxy clusters (see the review by Rosati et al. 2002).
Bonifacio Piercarlo
Bragaglia Angela
Carretta Eugenio
Castellani Vittorio
Centurion Martin
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