Generation of Magnetic Fields by the Stationary Accretion Shock Instability

TL;DR

This study investigates how the stationary accretion shock instability (SASI) can amplify magnetic fields in supernova environments, revealing significant magnetic energy growth through axisymmetric and nonaxisymmetric flows, with implications for neutron star magnetization.

Contribution

It demonstrates that SASI can substantially amplify magnetic fields via flow dynamics, especially in nonaxisymmetric spiral modes, providing new insights into magnetic field generation in supernovae.

Findings

Magnetic energy increases by about two orders of magnitude in axisymmetric simulations.

Nonaxisymmetric SASI modes amplify magnetic energy by nearly four orders of magnitude.

Magnetic field amplification does not qualitatively alter the global shock evolution.

Abstract

We begin an exploration of the capacity of the stationary accretion shock instability (SASI) to generate magnetic fields by adding a weak, stationary, and radial (but bipolar) magnetic field, and in some cases rotation, to an initially spherically symmetric fluid configuration that models a stalled shock in the post-bounce supernova environment. In axisymmetric simulations we find that cycles of latitudinal flows into and radial flows out of the polar regions amplify the field parallel to the symmetry axis, typically increasing the total magnetic energy by about two orders of magnitude. Nonaxisymmetric calculations result in fundamentally different flows and a larger magnetic energy increase: shearing associated with the SASI spiral mode contributes to a widespread and turbulent field amplification mechanism, boosting the magnetic energy by almost four orders of magnitude (a result which remains very sensitive to the spatial resolution of the numerical simulations). While the SASI may contribute to neutron star magnetization, these simulations do not show qualitatively new features in the global evolution of the shock as a result of SASI-induced magnetic field amplification.