Dissipation of magnetic fields in neutron star crusts due to development of a tearing mode

TL;DR

This paper investigates how tearing modes in Hall plasma can dissipate magnetic fields in neutron star crusts, potentially explaining the persistent X-ray emission observed in magnetars over tens of thousands of years.

Contribution

It introduces a model for tearing mode development in Hall plasma and estimates its growth rate, highlighting its role in magnetic field dissipation in magnetars.

Findings

Tearing mode growth rate peaks at an intermediate between resistive and Hall times.

Dissipation timescale of magnetic fields is estimated to be 10^4-10^5 years.

Tearing mode may power persistent X-ray emission in magnetars.

Abstract

Dissipation of magnetic fields in Hall plasma of neutron star crusts may power persistent high energy emission of a class of strongly magnetized neutrons stars, magnetars. We consider development of a dissipative tearing mode in Hall plasma (electron MHD) and find that its growth rate increases with the wave number of perturbations, reaching a maximum value intermediate between resistive $\tau_r$ and Hall times $\tau_H$, $\Gamma\sim 1 / \sqrt{\tau_r \tau_H}$. We argue that the tearing mode may be the principal mechanism by which strong magnetic fields are dissipated in magnetars on times scale of $\sim 10^4-10^5$ yrs powering the persistent X-ray emisison.