Neutron Star Crust Can Support A Large Ellipticity

TL;DR

This paper calculates the maximum ellipticity of neutron star crusts, indicating they can support larger deformations than previously thought, which enhances their potential as sources of continuous gravitational waves.

Contribution

It provides a new estimate of neutron star crust ellipticity using an improved formalism, suggesting stronger gravitational wave signals are possible.

Findings

Maximum ellipticity of 7.4×10^{-6} supports larger crust deformations.

Results are consistent with earlier studies, confirming the crust's capacity.

Neutron stars could be significant sources of continuous gravitational waves.

Abstract

Non-axisymmetrical deformations of the crust on rapidly rotating neutron stars are one of the main targets of searches for continuous gravitational waves. The maximum ellipticity, or fractional difference in moments of inertia, that can be supported by deformations of the crust (known as "mountains") provides an important upper limit on the strength of these continuous gravitational wave sources. We use the formalism of Gittins et al 2021, along with a deforming force that acts mainly in the transverse direction, to obtain a maximum ellipticity of 7.4$\times$10$^{-6}$. This is larger than the original results of Gittins et al 2021 but consistent with earlier calculations by Ushomirsky et al 2000. This suggests that rotating neutron stars could be strong sources of continuous gravitational waves.