Evolution of Close Binaries and the Formation of Pulsars

Abstract

The various ways in which compact objects (neutron stars and black holes) can be formed in interacting binary systems are outlined. It is argued that most of the remnants of massive stars (M1 ≳ 10 M⊙) will be runaway pulsars, with space velocities ≳ 100 km/s, i.e.: (i)semi-conservatively evolving massive close binaries (~ 1/3 of all massive stars) after the first SN explosion consist of a massive star and a neutron star; subsequently, after a stage of common-envelope evolution and spiral-in most of these systems are disrupted in the second SN, producing two runaway pulsars, one young and one old.(ii)highly non-conservatively evolving systems (with initial mass ratio q0 ≲ 0.5 and binary periods up to several decades; ≳ 1/3 of all massive stars) will spiral-in during the first phase of mass transfer and are disrupted in the first SN explosion, producing one young runaway pulsar, together with a runaway star of low or moderate mass.