Direct simulations of a supernova-driven galactic dynamo

TL;DR

This paper demonstrates through direct simulations that supernova-driven turbulence combined with shear can exponentially amplify galactic magnetic fields, overcoming previous models' limitations on vertical transport.

Contribution

It provides the first direct numerical evidence that supernova activity can effectively drive a galactic dynamo, highlighting the role of turbulent pumping and galactic winds.

Findings

Supernova-driven turbulence leads to exponential magnetic field amplification.

Turbulent pumping is inward and balanced by galactic wind.

Dynamo action is facilitated by shear and supernova activity.

Abstract

Supernovae are known to be the dominant energy source for driving turbulence in the interstellar medium. Yet, their effect on magnetic field amplification in spiral galaxies is still poorly understood. Previous analytical models, based on the evolution of isolated, non-interacting supernova remnants, predicted a dominant vertical pumping that would render dynamo action improbable. In the present work, we address the issue of vertical transport, which is thought to be the key process that inhibits dynamo action in the galactic context. We aim to demonstrate that supernova driving is a powerful mechanism to amplify galactic magnetic fields. We conduct direct numerical simulations in the framework of resistive magnetohydrodynamics. Our local box model of the interstellar medium comprises optically-thin radiative cooling, an external gravitational potential, and background shear. Dynamo coefficients for mean-field models are measured by means of passive test fields. Our simulations show that supernova-driven turbulence in conjunction with shear leads to an exponential amplification of the mean magnetic field. We found turbulent pumping to be directed inward and approximately balanced by a galactic wind.