On the Shear Instability in Relativistic Neutron Stars

TL;DR

This study demonstrates that differentially rotating neutron stars can develop shear instabilities at lower T/|W| ratios than previously thought, which may significantly impact gravitational wave emission.

Contribution

The paper provides the first evidence of shear instabilities occurring in rapidly rotating neutron stars below the classical bar-mode threshold in full general relativity.

Findings

Shear instabilities occur at T/|W| below 0.25 in differentially rotating stars.

These instabilities develop on a dynamical timescale.

Potentially stronger gravitational wave sources than previously identified.

Abstract

We present new results on instabilities in rapidly and differentially rotating neutron stars. We model the stars in full general relativity and describe the stellar matter adopting a cold realistic equation of state based on the unified SLy prescription. We provide evidence that rapidly and differentially rotating stars that are below the expected threshold for the dynamical bar-mode instability, beta_c = T/|W| ~ 0.25, do nevertheless develop a shear instability on a dynamical timescale and for a wide range of values of beta. This class of instability, which has so far been found only for small values of beta and with very small growth rates, is therefore more generic than previously found and potentially more effective in producing strong sources of gravitational waves. Overall, our findings support the phenomenological predictions made by Watts, Andersson and Jones on the nature of the low-T/|W|.