Binary evolution and neutron stars in globular clusters

Abstract

Improved observations of globular clusters are uncovering a large number of radio pulsars and of X-ray sources. The latter include binaries in which a neutron star or a white dwarf accretes matter from a companion, recycled pulsars, and magnetically active binaries. Most of these sources originate from close encounters between stars in the cluster core; magnetically active binaries and some cataclysmic variables have evolved from primordial binaries. The formation rate through close encounters scales differently with the central density and core radius of the cluster than the probability for a single binary to be perturbed by an encounter. This is exploited in some preliminary observational tests of the close encounter hypothesis. Accreting black holes have been found in globular clusters with other galaxies; the absence of such holes in the Milky Way clusters is compatible with the small number expected.