Evolution of close neutron star binaries

Abstract

In binary systems consisting of two neutron stars, the orbit decays by gravitational radiation. A crude model shows that the less massive star may suffer either immediate tidal disruption or slow mass stripping when it reaches its Roche radius, depending on the initial masses and on the details of mass exchange or mass loss. Typical energy releases are 4 x 10 to the 52 ergs in gravitational waves before the onset of stripping, 2 x 10 to the 52 ergs in gravitational waves after the onset of stripping, 2 x 10 to the 53 ergs in neutrinos after the onset of stripping. The stripping process always ends in tidal disruption of the less massive star after a few seconds or a few hundred revolutions. As the endpoint of binary stellar evolution, such events are estimated to occur only about every 100 yr out to a radius of 15 Mpc, and are thus less important than supernovae as sources of gravitational waves; the observed wave amplitude would be about 10 to the -21. Such events may occur in Type II supernovae, if the collapsing stellar core rotates rapidly enough to fission into two neutron stars.