The Breaking Strain of Neutron Star Crust and Gravitational Waves

TL;DR

This study uses molecular dynamics simulations to determine that neutron star crusts are extremely strong and capable of supporting large mountains, which could emit detectable gravitational waves and influence neutron star spin limits.

Contribution

The paper provides the first detailed microscopic modeling of neutron star crust strength, showing impurities and defects modestly reduce the breaking strain, with implications for gravitational wave emission.

Findings

Neutron star crust has a very high breaking strain (~0.1).

Impurities and defects modestly reduce crust strength.

Strong crusts can support mountains large enough for detectable gravitational waves.

Abstract

Mountains on rapidly rotating neutron stars efficiently radiate gravitational waves. The maximum possible size of these mountains depends on the breaking strain of neutron star crust. With multi-million ion molecular dynamics simulations of Coulomb solids representing the crust, we show that the breaking strain of pure single crystals is very large and that impurities, defects, and grain boundaries only modestly reduce the breaking strain to around 0.1. Due to the collective behavior of the ions during failure found in our simulations, the neutron star crust is likely very strong and can support mountains large enough so that their gravitational wave radiation could limit the spin periods of some stars and might be detectable in large scale interferometers. Furthermore, our microscopic modeling of neutron star crust material can help analyze mechanisms relevant in magnetar giant and micro flares.