Oscillations of rapidly rotating stratified neutron stars

TL;DR

This paper investigates the oscillation modes of rapidly rotating neutron stars, focusing on the effects of stratification and rotation on g-modes and inertial modes, with implications for gravitational-wave instabilities.

Contribution

It introduces a detailed analysis of g-modes in fast-spinning neutron stars, highlighting their transformation into inertial modes as rotation increases.

Findings

G-modes become rotation-dominated at high spin rates

Comparison between stratified and non-stratified models clarifies mode behavior

Insights into gravitational-wave driven instabilities of oscillation modes

Abstract

We use time-evolutions of the linear perturbation equations to study the oscillations of rapidly rotating neutrons stars. Our models account for the buoyancy due to composition gradients and we study, for the first time, the nature of the resultant g-modes in a fast spinning star. We provide detailed comparisons of non-stratified and stratified models. This leads to an improved understanding of the relationship between the inertial modes of a non-stratified star and the g-modes of a stratified system. In particular, we demonstrate that each g-mode becomes rotation-dominated, i.e. approaches a particular inertial mode, as the rotation rate of the star is increased. We also discuss issues relating to the gravitational-wave driven instability of the various classes of oscillation modes.