A theory for the origin of globular clusters

The authors present a theory for the origin of globular clusters during the collapse of a protogalaxy. A thermal instability promotes the development of a two-phase structure in the gas when the cooling time is comparable to the free-fall time. The hot component, which remains near the virial temperature, compresses the cold component into discrete clouds with temperatures near 104K and mean densities in the range 1 - 10 Mₛun;pc-3. It is shown that the initial amplitudes of the perturbations required to produce such clouds are of order 10%. When the abundance of heavy elements is less than 10-2Zₛun;, further cooling is inefficient and the minimum mass for gravitational instability is of order 106Mₛun;. The authors compare these predictions with the observed properties of globular clusters and find satisfactory agreement, especially if there is some mass loss.