Instability of magnetic equilibria in barotropic stars
Mitchell, J. P.
Valdivia Hepp, Juan
Cita de ítem
MNRAS 447, 1213–1223 (2015)
Artículo de publicación ISI
In stably stratified stars, numerical magnetohydrodynamics simulations have shown that arbitrary
initial magnetic fields evolve into stable equilibrium configurations, usually containing
nearly axisymmetric, linked poloidal and toroidal fields that stabilize each other. In this work,
we test the hypothesis that stable stratification is a requirement for the existence of such
stable equilibria. For this purpose, we follow numerically the evolution of magnetic fields
in barotropic (and thus neutrally stable) stars, starting from two different types of initial
conditions, namely random disordered magnetic fields, as well as linked poloidal–toroidal
configurations resembling the previously found equilibria. With many trials, we always find a
decay of the magnetic field over a few Alfv´en times, never a stable equilibrium. This strongly
suggests that there are no stable equilibria in barotropic stars, thus clearly invalidating the assumption
of barotropic equations of state often imposed on the search of magnetic equilibria.
It also supports the hypothesis that, as dissipative processes erode the stable stratification, they
might destabilize previously stable magnetic field configurations, leading to their decay.
DFG-CONICYT International Collaboration
Grant DFG-06, FONDECYT Regular Project 1110213
and Proyecto de Financiamiento Basal PFB-06/2007