On non-axisymmetric magnetic equilibria in stars

TL;DR

This paper explores the formation of stable, non-axisymmetric magnetic field configurations in stars through numerical simulations, revealing conditions that lead to complex equilibria like twisted flux tubes, which may explain observed stellar magnetic anomalies.

Contribution

It demonstrates the existence of stable non-axisymmetric magnetic equilibria in stars and identifies the initial magnetic field profile conditions necessary for their formation.

Findings

Non-axisymmetric equilibria with twisted flux tubes can form and remain stable.

The formation depends on the initial magnetic field's radial profile.

Results may explain observed non-dipolar stellar magnetic fields.

Abstract

In previous work stable approximately axisymmetric equilibrium configurations for magnetic stars were found by numerical simulation. Here I investigate the conditions under which more complex, non-axisymmetric configurations can form. I present numerical simulations of the formation of stable equilibria from turbulent initial conditions and demonstrate the existence of non-axisymmetric equilibria consisting of twisted flux tubes lying horizontally below the surface of the star, meandering around the star in random patterns. Whether such a non-axisymmetric equilibrium or a simple axisymmetric equilibrium forms depends on the radial profile of the strength of the initial magnetic field. The results could explain observations of non-dipolar fields on stars such as the B0.2 main-sequence star tau-Sco or the pulsar 1E 1207.4-5209. The secular evolution of these equilibria due to Ohmic and buoyancy processes is also examined.