From X-ray binaries to binary and millisecond pulsars

Abstract

Observational evidence on binary and millisecond pulsars indicates that these neutrons starts have been “recycled” in binary systems, i.e. have been spun up by accretion after substantial decay of their surface magnetic fields. There are two groups of binary pulsars, the PSR 1913+16-group, which descended from massive X-ray binaries, and the PSR 1953+29-group, which descended from fairly wide low-mass X-ray binaries. At least several neutron stars in the second group have formed by the accretion-induced collapse of a massive white dwarf. The companion stars in both group of systems are expected to be dead stars, i.e. white dwarfts or neutron stars. The large total number of millisecond binary pulsars in the galaxy (≈10 4), indicates that magnetic fields of nuetron starts do not decay below a value of order 10 9 G. Single millisecond pulsars may have lost their companions in various ways. In globular clusters this is most likely to have happened as a conseqeunce of a collision induced by the passage of a third star. Of order 10 2 single millisecond pulsars may have been formed in this way, of which about one third escaped from their clusters. Single millisecond pulsars outside globular clusters may also have formed by coalescence with a close companion, most probably a white dwarf.