On the origin of low-mass x-ray binaries

Abstract

Several evolutionary scenarios have been proposed for the origin of low‐mass x‐ray binaries, including accretion‐induced collapse, common envelope evolution of a massive binary with an extreme mass ratio, black hole formation in Wolf‐Rayet binaries with extreme mass ratios, triple star evolution, and (in globular clusters) tidal capture. In this brief review, we examine some of the factors which determine whether a primordial binary may survive to become a neutron star‐ or black hole‐binary with a low‐mass nondegenerate component, and what structural criteria it must satisfy, having reached that state, in order to appear as an x‐ray binary. These constraints include: survival of common envelope evolution, survival of the supernova or core‐collapse event, duration of the non‐interactive phase following formation of the compact component and evolutionary state of the donor star, and finally the critical mass ratios which dictate the time scale for mass transfer in the x‐ray state. A population synthesis model for newly‐formed LMXBs illustrates a number of these constraints.