New class of g-modes and unexpected convection in neutron stars

TL;DR

This paper introduces a new class of low-frequency g-modes in superfluid neutron stars, analyzes their stability, and discusses implications for neutron star cooling and seismology.

Contribution

It identifies a novel class of g-modes, derives their stability criterion, and explores their dependence on the equation of state and superfluidity models.

Findings

New g-modes can be unstable to convection.

Convection may occur for both positive and negative temperature gradients.

Implications for neutron star cooling and seismology.

Abstract

We suggest a specific new class of low-frequency g-modes in superfluid neutron stars. We determine the Brunt-Vaisala frequency for these modes and demonstrate that they can be unstable with respect to convection. The criterion for the instability onset (analogue of the well known Schwarzschild criterion) is derived. It is very sensitive to equation of state and a model of nucleon superfluidity. In particular, convection may occur for both positive and negative temperature gradients. Our results have interesting implications for neutron star cooling and seismology.