Origin and evolution of X-ray binaries in globular clusters

Abstract

The theoretical model developed by Grindlay (1984 and 1985) and Grindlay and Hertz (1985) to explain the relative numbers of low-luminosity and high-luminosity X-ray sources in Galactic globular clusters is briefly characterized, and the relevant observational evidence is summarized. In the model, high-rate mass transfer onto white dwarfs in about 1 percent of the low-luminosity binary sources produces neutron stars, which then form compact high-luminosity X-ray binaries (by tidal capture in the dense cluster cores); these in turn evolve into hierarchical triple systems. Evidence considered includes observations of the high-luminosity giant-fed X-ray binary in M 15, the results of searches for CVs in globulars, comparisons of X-ray-binary and host-globular evolution, and indications that GX 17 + 2 is a bound triple.