Properties of r modes in rotating magnetic neutron stars. II. Evolution of the r modes and stellar magnetic field

TL;DR

This paper investigates how the evolution of r-mode instabilities in rotating neutron stars interacts with magnetic fields, potentially suppressing gravitational wave signals, especially in stars with initial magnetic fields above 10^10 G.

Contribution

It provides a numerical analysis of magnetic field evolution due to r-mode induced differential rotation and assesses its effect on gravitational wave detectability.

Findings

Large-scale toroidal magnetic fields can be generated by r-mode evolution.

Strong initial magnetic fields (>10^10 G) can significantly reduce gravitational wave signals.

The evolution equations for magnetic fields are numerically solved to estimate suppression conditions.

Abstract

The evolution of the r-mode instability is likely to be accompanied by secular kinematic effects which will produce differential rotation with large scale drifts of fluid elements, mostly in the azimuthal direction. As first discussed by Rezzolla, Lamb and Shapiro 2000, the interaction of these secular velocity fields with a pre-existing neutron star magnetic field could result in the generation of intense and large scale toroidal fields. Following their derivation in the companion paper, we here discuss the numerical solution of the evolution equations for the magnetic field. The values of the magnetic fields obtained in this way are used to estimate the conditions under which the r-mode instability might be prevented or suppressed. We also assess the impact of the generation of large magnetic fields on the gravitational wave detectability of r-mode unstable neutron stars. Our results indicate that the signal to noise ratio in the detection of gravitational waves from the r-mode instability might be considerably decreased if the latter develops in neutron stars with initial magnetic fields larger than 10^10 G.