Gravitational Radiation Instability in Hot Young Neutron Stars

TL;DR

This paper demonstrates that gravitational radiation causes an instability in hot, young, rapidly rotating neutron stars, which can significantly slow their rotation by emitting gravitational waves within about a year.

Contribution

It identifies the dominant l=2 r-mode instability as a mechanism for angular momentum loss in young neutron stars due to gravitational radiation.

Findings

The instability can reduce the star's rotation to about 7.6% of the Keplerian rate within a year.

Viscous effects suppress the instability in older, colder neutron stars.

The instability primarily affects hot, young neutron stars with rapid rotation.

Abstract

We show that gravitational radiation drives an instability in hot young rapidly rotating neutron stars. This instability occurs primarily in the l=2 r-mode and will carry away most of the angular momentum of a rapidly rotating star by gravitational radiation. On the timescale needed to cool a young neutron star to about T=10^9 K (about one year) this instability can reduce the rotation rate of a rapidly rotating star to about 0.076\Omega_K, where \Omega_K is the Keplerian angular velocity where mass shedding occurs. In older colder neutron stars this instability is suppressed by viscous effects, allowing older stars to be spun up by accretion to larger angular velocities.