Supernova-driven Turbulence and Magnetic Field Amplification in Disk Galaxies

TL;DR

This paper uses direct simulations to show that supernova-driven turbulence can rapidly amplify magnetic fields in disk galaxies, challenging previous analytical predictions and emphasizing the role of galactic rotation in dynamo processes.

Contribution

It demonstrates, through simulations, that supernova-driven turbulence can cause exponential magnetic field amplification within 100 million years, confirming the classical dynamo theory.

Findings

Supernova-driven turbulence leads to exponential magnetic field amplification.

Vertical stratification and galactic rotation are crucial for the dynamo process.

Rotation-induced helicity is essential for sustained magnetic field growth.

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. Analytical models based on the uncorrelated-ensemble approach predicted that any created field will be expelled from the disk before a significant amplification can occur. By means of direct simulations of supernova-driven turbulence, we demonstrate that this is not the case. Accounting for vertical stratification and galactic differential rotation, we find an exponential amplification of the mean field on timescales of 100Myr. The self-consistent numerical verification of such a "fast dynamo" is highly beneficial in explaining the observed strong magnetic fields in young galaxies. We, furthermore, highlight the importance of rotation in the generation of helicity by showing that a similar mechanism based on Cartesian shear does not lead to a sustained amplification of the mean magnetic field. This finding impressively confirms the classical picture of a dynamo based on cyclonic turbulence.