Hydromagnetic Instabilities in Neutron Stars

TL;DR

This paper models the non-linear magnetohydrodynamics of poloidal magnetic fields in neutron stars, revealing the dominance of kink instabilities and the emergence of stable non-axisymmetric equilibria with implications for magnetar phenomena.

Contribution

It provides a detailed analysis of hydromagnetic instabilities in neutron stars using general relativistic MHD simulations, highlighting the role of kink instabilities and stable equilibria.

Findings

Kink instability dominates the magnetic field evolution.

Neutron stars can reach stable non-axisymmetric quasi-equilibria.

Implications for magnetar flare mechanisms and oscillations.

Abstract

We model the non-linear ideal magnetohydrodynamics of poloidal magnetic fields in neutron stars in general relativity assuming a polytropic equation of state. We identify familiar hydromagnetic modes, in particular the 'sausage/varicose' mode and 'kink' instability inherent to poloidal magnetic fields. The evolution is dominated by the kink instability, which causes a cataclysmic reconfiguration of the magnetic field. The system subsequently evolves to new, non-axisymmetric, quasi-equilibrium end-states. The existence of this branch of stable quasi-equilibria may have consequences for magnetar physics, including flare generation mechanisms and interpretations of quasi-periodic oscillations.