Finite-Element Simulations of Rotating Neutron Stars with Anisotropic Crusts and Continuous Gravitational Waves

TL;DR

This paper uses finite-element simulations to study how anisotropic crusts in rotating neutron stars can produce detectable continuous gravitational waves, potentially explaining observed pulsar phenomena.

Contribution

It introduces three-dimensional finite-element modeling of anisotropic neutron star crusts to assess gravitational wave emission, advancing previous simpler models.

Findings

Anisotropic crusts can support ellipticities of a few 10^{-9}.

Detected gravitational waves could originate from such crustal deformations.

Results align with observational bounds on pulsar ellipticities.

Abstract

``Mountains'', or non-axisymmetrical deformations in the elastic crust of rotating neutron stars are efficient radiators of continuous gravitational waves. Recently, small anisotropies were observed in the solid innermost inner core of the Earth. We implement three-dimensional finite-element simulations to study mountains sourced by modest anisotropies in the solid crust of rotating neutron stars. We find that anisotropic mountains may be detectable by current ground-based gravitational-wave detectors and might explain several observed phenomena, confirming the results of a previous work on less realistic neutron star models. In particular, we find that a slightly anisotropic neutron star crust that changes its rotation rate modestly can support an ellipticity of a few $\times$ 10$^{-9}$, which is equivalent to the upper bounds on the ellipticity of some nearby and rapidlly spinning pulsars.