On the Stability of Non Force-Free Magnetic Equilibria in Stars

TL;DR

This paper demonstrates through simulations that certain analytically derived mixed magnetic equilibria in stars are stable, unlike their purely poloidal or toroidal counterparts, supporting their role in stellar magnetic stability.

Contribution

It provides the first stability test of an analytically derived non force-free magnetic equilibrium in stars using 3D MHD simulations.

Findings

Mixed equilibrium shows no instability under perturbations.

Purely poloidal and toroidal configurations are unstable.

Mixed configurations are suitable for modeling stellar magnetic fields.

Abstract

The existence of stable magnetic configurations in white dwarfs, neutron stars and various non-convective stellar {regions} is now well recognized. It has recently been shown numerically that various families of equilibria, including axisymmetric mixed poloidal-toroidal configurations, are stable. Here we test the stability of an analytically-derived non force-free magnetic equilibrium, using three-dimensional magnetohydrodynamic simulations: the mixed configuration is compared with the dynamical evolution of its purely poloidal and purely toroidal components, both known to be unstable. The mixed equilibrium shows no sign of instability under white noise perturbations. {This configuration therefore provides a good description of magnetic equilibrium topology inside non-convective stellar objects and will be useful to initialize magneto-rotational transport in stellar evolution codes.