Gravitational radiation from a solid-crust neutron star

Abstract

The measured period derivative1–3 for the millisecond pulsar PSR1937 + 214 is Ṗ ≃ 1.05×10−19, whereas the present upper limit5 for PSR1953 + 296 is Ṗ<4.2×10−17. For electromagnetic braking, the combination of rapid rotation with such small period derivatives requires a small (∼108 G) magnetic field. A natural association between rapid rotation and small magnetic field is provided by accretion spin-up scenarios7–9. Here we address the analogous problem for gravitational radiation. Balancing gravitational radiation power against the rate of rotational energy loss, we find that if the effective triaxiality eeff exceeds emax∼10−9, gravitational radiation alone would spin a millisecond pulsar down at a faster rate than the observed Ṗ. We show that eeff<<emax, so that gravitational radiation is not likely to play a major role in the evolution of millisecond pulsars even in the absence of damping. Damping times for precession of the solid crust are estimated to be <2×l03 yr.