# Instability of twisted magnetar magnetospheres

## TL;DR

This paper uses 3D simulations to identify an instability in twisted magnetar magnetospheres, revealing a mechanism for energy release and crustal stress that may explain giant flares.

## Contribution

It introduces a new instability criterion for magnetar magnetospheres based on force-free electrodynamics simulations, highlighting a previously unknown unstable branch of solutions.

## Key findings

- Up to 30% of magnetospheric energy dissipated during instability
- Magnetic field rearrangement triggers crustal stresses and potential failure
- Results align with observed giant flare energies and emissions

## Abstract

We present three-dimensional force-free electrodynamics simulations of magnetar magnetospheres that demonstrate the instability of certain degenerate, high energy equilibrium solutions of the Grad-Shafranov equation. This result indicates the existence of an unstable branch of twisted magnetospheric solutions and allows to formulate an instability criterion. The rearrangement of magnetic field lines as a consequence of this instability triggers the dissipation of up to 30% of the magnetospheric energy on a thin layer above the magnetar surface. During this process, we predict an increase of the mechanical stresses onto the stellar crust, which can potentially result in a global mechanical failure of a significant fraction of it. We find that the estimated energy release and the emission properties are compatible with the observed giant flare events. The newly identified instability is a candidate for recurrent energy dissipation, which could explain part of the phenomenology observed in magnetars.