Mountain formation by repeated, inhomogeneous crustal failure in a neutron star

TL;DR

This paper models the repeated crustal failure in neutron stars using a cellular automaton to predict failure events, gravitational wave signals, and their implications for star spin-down and observational detection.

Contribution

It introduces a novel inhomogeneous crust failure model for neutron stars based on cellular automata, linking failure dynamics to gravitational wave predictions.

Findings

Failure event size and timing distributions are characterized.

Star's ellipticity and gravitational wave strain are predicted over its lifespan.

Failure rate increases as the star spins down to about 1% of initial frequency.

Abstract

The elastic crust of a neutron star fractures repeatedly as it spins down electromagnetically. An idealised, macroscopic model of inhomogeneous crustal failure is presented based on a cellular automaton with nearest-neighbour tectonic interactions involving strain redistribution and thermal dissipation. Predictions are made of the size and waiting-time distributions of failure events, as well as the rate of failure as the star spins down. The last failure event typically occurs when the star spins down to approximately 1% of its birth frequency with implications for rotational glitch activity. Neutron stars are commonly suggested as sources of continuous gravitational waves. The output of the automaton is converted into predictions of the star's mass ellipticity and gravitational wave strain as functions of its age, with implications for future observations with instruments such as the Laser Interferometer Gravitational Wave Observatory (LIGO), the Virgo interferometer, or the Kamioka Gravitational Wave Detector (KAGRA).