Gravitational wave emission from rotating superfluid neutron stars

TL;DR

This paper explores how pinned superfluid components in rotating neutron stars can produce gravitational waves at both the star's spin frequency and its first harmonic, suggesting new search strategies for gravitational wave detection.

Contribution

It introduces the novel idea that superfluid pinning allows gravitational wave emission at both $\, ext{Ω}$ and $2 ext{Ω}$, unlike the conventional case.

Findings

Superfluid pinning enables dual harmonic gravitational wave emission.

Targeted searches should include both $\, ext{Ω}$ and $2 ext{Ω}$ harmonics.

Detection of such signals would confirm superfluid pinning inside neutron stars.

Abstract

In this paper we investigate the effect of a pinned superfluid component on the gravitational wave emission of a steadily rotating deformed neutron star. We show that the superfluid pinning allows the possibility for there to be gravitational wave emission at both the stellar spin frequency $\Omega$ and its first harmonic, $2\Omega$. This contrasts with the conventional case where there is no pinned superfluidity, where either only the $2\Omega$ harmonic is present, or else the star undergoes precession, a feature which is not believed to be common in the known pulsar population. This work motivates the carrying out of gravitational wave searches where both the $\Omega$ and $2\Omega$ harmonics are searched for, even in targeted searches for waves from known pulsars which aren't observed to precess. Observation of such a two-component signal would provide evidence in favour of pinned superfluidity inside the star.