Nonaxisymmetric Hall instability: A key to understanding magnetars

Abstract

It is generally accepted that the nonlinear, dynamical evolution of magnetic fields in the interior of neutron stars plays a key role in the explanation of the observed phenomenology. Understanding the transfer of energy between toroidal and poloidal components, or between different scales, is of particular relevance. In this Rapid Communication, we present the first three-dimensional (3D) simulations of the Hall instability in a neutron star crust, confirming its existence for typical magnetar conditions. We compare our results to estimates obtained by a linear perturbation analysis, which discards any interpretation as numerical instabilities and confirms its physical origin. Interestingly, the Hall instability creates locally strong magnetic structures that occasionally can make the crust yield to the magnetic stresses and generates coronal loops, similar to the way solar coronal loops find their way out through the photosphere. This supports the viability of the mechanism, which has been proposed to explain magnetar outbursts.