Modelling neutron star mountains

TL;DR

This paper reviews and critiques existing models of neutron star mountains, introduces a new modeling scheme considering various force descriptions, and finds that maximum quadrupoles are significantly smaller than previous estimates, impacting gravitational wave detection prospects.

Contribution

It presents a novel scheme for modeling neutron star mountains that accounts for different force descriptions, refining estimates of maximum quadrupole moments.

Findings

Maximum quadrupoles are 2-100 times smaller than previous estimates.

New models consider diverse force sources like potential solutions and thermal pressures.

Implications for gravitational wave detectability of neutron star deformations.

Abstract

As the era of gravitational-wave astronomy has well and truly begun, gravitational radiation from rotating neutron stars remains elusive. Rapidly spinning neutron stars are the main targets for continuous-wave searches since, according to general relativity, provided they are asymmetrically deformed, they will emit gravitational waves. It is believed that detecting such radiation will unlock the answer to why no pulsars have been observed to spin close to the break-up frequency. We review existing studies on the maximum mountain that a neutron star crust can support, critique the key assumptions and identify issues relating to boundary conditions that need to be resolved. In light of this discussion, we present a new scheme for modelling neutron star mountains. The crucial ingredient for this scheme is a description of the fiducial force which takes the star away from sphericity. We consider three examples: a source potential which is a solution to Laplace's equation, another solution which does not act in the core of the star and a thermal pressure perturbation. For all the cases, we find that the largest quadrupoles are between a factor of a few to two orders of magnitude below previous estimates of the maximum mountain size.