THE AGE OF THE GLOBULAR-CLUSTERS

Globular clusters are compact groups of stars found in the haloes of g alaxies. For the clusters in the Milky Way, a combination of the best available observational data and models of stellar evolution indicates that they are among the oldest objects in our Galaxy, with an age of approximately 13 billion years. this age roughly coincides with recent estimates of the age of a low-density, freely expanding Universe. The ages of the globular clusters may therefore provide a critical test o f cosmological models, although this must await more accurate distance (and hence age) determinations. Improved age estimates should also he lp determine whether the halo of our Galaxy formed from accreted dwarf galaxies or through the collapse of a spherical protogalactic cloud.