Limiting Rotation Rate of Neutron Stars from Crust Breaking and Gravitational Waves

TL;DR

This paper investigates how crust failure in neutron stars limits their rotation speed and explores the potential for gravitational wave emission to further restrict their spin, highlighting implications for gravitational wave detection.

Contribution

The study combines finite-element simulations with theoretical analysis to show crust failure occurs at half the breakup rate, suggesting a new mechanism for spin limitation and gravitational wave emission.

Findings

Crust fails at about half the breakup rotation rate.

Asymmetric crust failure may induce ellipticity and gravitational waves.

Potential gravitational wave signals from spinning neutron stars could be detectable.

Abstract

Neutron stars are not observed to spin faster than about half their breakup rate. This limiting rotational frequency may be related to the strength of their crusts. As a star spins up from accretion, centrifugal forces stress the crust. We perform finite-element simulations of rotating neutron stars and find that the crust fails at rotation rates about half the breakup rate. Given uncertainties in microphysics, we have not determined the crust configuration after this failure. Instead, we argue that the crust may fail in an asymmetric way and could produce a configuration with a significant ellipticity (fractional difference in moments of inertia). If the ellipticity is large, a rotating star will radiate gravitational waves that may limit further spin up. These stars may be promising sources for LIGO / VIRGO and next generation gravitational wave detectors.