Radiation-Driven Evolution of Low-Mass X-Ray Binaries and the Formation of Millisecond Pulsars

Abstract

Recent data on low-mass X-ray binaries (LMXBs) and millisecond pulsars (MSPs) pose a challenge to evolutionary theories which neglect the effects of disk and companion irradiation. Here we discuss the main features of a radiation-driven (RD) evolutionary model that may be applicable to several LMXBs. According to this model, radiation from the accreting compact star in LMXBs ‘vaporizes’ the accretion disk and the companion star by driving a self-sustained mass loss until a sudden accretion-turn off occurs. The main characteristics of the RD-evolution are: (1) the lifetime of RD-LMXB’s is of order 107 years or less; (2) both the orbital period gap and the X-ray luminosity may be consequences of RD-evolution of LMXB’s containing lower main sequence and degenerate companion stars; (3) the companion star may transfer mass to the primary even if it underfills its Roche lobe; (4) a class of recycled MSPs can continue to vaporize the low-mass companions by a strong pulsar wind even after the accretion turn-off; (5) the RD-evolutionary model resolves the apparent statistical discrepancy between the number of MSPs and their LMXB progenitors in the Galaxy. We discuss the implications of the discovery of single MSPs in low-density globular clusters and the recent measurements of short orbital timescales of four LMXBs.KeywordsOrbital PeriodNeutron StarSmooth Particle HydrodynamicGlobular ClusterCompanion StarThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.