Damping of GRR instability by direct URCA reactions

TL;DR

This paper analyzes how direct URCA reactions contribute to damping gravitational radiation-driven instabilities in neutron stars, calculating the temperature at which bulk viscosity suppresses the instability, and showing that direct URCA reactions significantly reduce the instability region.

Contribution

It provides an analytical calculation of the damping effect of direct URCA reactions on gravitational radiation instabilities in neutron stars, extending previous work on bulk viscosity effects.

Findings

Direct URCA reactions significantly reduce the temperature and rotation frequency range of GRR instability.

The temperature for complete suppression of the instability is explicitly calculated.

Bulk viscosity from direct URCA reactions is more effective than modified URCA processes in damping the instability.

Abstract

The role of direct URCA reactions in damping of the gravitational radiation driven instability is discussed. The temperature at which bulk viscosity suppresses completely this instability is calculated. The results are obtained analytically using recent calculations performed in the case of bulk viscosity due to the modified URCA processes (Lindblom 1995; Yoshida & Eriguchi 1995). The bulk viscosity caused by direct URCA reactions is found to reduce significantly the region of temperatures and rotation frequencies where a neutron star is subject to GRR instability.