Does elasticity stabilise a magnetic neutron star?

TL;DR

This paper investigates whether the elastic properties of a neutron star's crust can stabilize its magnetic field configurations, which are otherwise unstable in simplified models, by analyzing the critical shear modulus needed for stability.

Contribution

It introduces the effect of crust elasticity into magnetic stability analysis of neutron stars, providing a criterion for stabilization against magnetic instabilities.

Findings

Elasticity can stabilize magnetic configurations in neutron stars.

A critical shear modulus value is identified for stability.

Implications for neutron star magnetic field evolution.

Abstract

The configuration of the magnetic field in the interior of a neutron star is mostly unknown from observations. Theoretical models of the interior magnetic field geometry tend to be oversimplified to avoid mathematical complexity and tend to be based on axisymmetric barotropic fluid systems. These static magnetic equilibrium configurations have been shown to be unstable on a short time scale against an infinitesimal perturbation. Given this instability, it is relevant to consider how more realistic neutron star physics affects the outcome. In particular, it makes sense to ask if elasticity, which provides an additional restoring force on the perturbations, may stabilise the system. It is well-known that the matter in the neutron star crust forms an ionic crystal. The interactions between the crystallized nuclei can generate shear stress against any applied strain. To incorporate the effect of the crust on the dynamical evolution of the perturbed equilibrium structure, we study the effect of elasticity on the instability of an axisymmetric magnetic star. In particular we determine the critical shear modulus required to prevent magnetic instability and consider the corresponding astrophysical consequences.