Asteroseismology of rapidly rotating neutron stars - an alternative approach

TL;DR

This paper develops new gravitational wave asteroseismology relations for rapidly rotating neutron stars using an alternative approach that improves equation of state independence and enables accurate inverse parameter estimation from observed frequencies.

Contribution

It introduces a novel method using the moment of inertia and different normalization to enhance universality of asteroseismology relations for rotating neutron stars.

Findings

Stronger equation of state independence in non-rotating case.

Accurate inverse problem solution with three frequencies for rotating stars.

Relations are effective for massive, secularly unstable neutron star models.

Abstract

In the present paper we examine gravitational wave asteroseismology relations for f-modes of rapidly rotating neutron stars. An approach different to the previous studies is employed - first, the moment of inertia is used instead of the stellar radius, and second, the normalization of the oscillation frequencies and damping times is different. It was shown that in the non-rotating case this can lead to a much stronger equation of state independence and our goal is to generalize the static relations to the rapidly rotating case and values of the spherical mode number $l\ge2$. We employ realistic equations of state that cover a very large range of stiffness in order to check better the universality of the relations. At the end we explore the inverse problem, i.e. obtain the neutron star parameters from the observed gravitational frequencies and damping times. It turns out that with this new set of relations we can solve the inverse problem with a very good accuracy using three frequencies that was not possible in the previous studies where one needs also the damping times. The asteroseismology relations are also particularly good for the massive rapidly rotating models that are subject to secular instabilities.