Global simulations of galactic dynamo driven by cosmic-rays and exploding magnetized stars

TL;DR

This paper presents global MHD simulations showing how cosmic-ray driven dynamo processes can amplify small-scale magnetic fields from supernovae into large-scale galactic magnetic fields, matching observed equipartition levels.

Contribution

It introduces a new simulation approach demonstrating the amplification and large-scale organization of magnetic fields via cosmic-ray driven dynamo mechanisms.

Findings

Small-scale dipolar fields are exponentially amplified.

Magnetic fields are transferred to large scales through inverse cascade.

Simulations match observed galactic magnetic field strengths.

Abstract

We conduct global galactic--scale magnetohydrodynamical (MHD) simulations of the cosmic--ray driven dynamo. We assume that exploding stars deposit small--scale, randomly oriented, dipolar magnetic fields into the differentially rotating ISM, together with a portion of cosmic rays, accelerated in supernova shocks. Our simulations are performed with the aid of a new parallel MHD code PIERNIK. We demonstrate that dipolar magnetic fields supplied on small SN--remnant scales, can be amplified exponentially by the CR--driven dynamo to the present equipartition values, and transformed simultaneously to large galactic--scales by an inverse cascade promoted by resistive processes.