Cosmic-ray driven dynamo in galaxies

TL;DR

This paper discusses advanced numerical models of the cosmic-ray driven dynamo in galaxies, showing how cosmic rays and supernovae contribute to large-scale magnetic field amplification resembling observed galactic structures.

Contribution

It introduces detailed CR+MHD simulations that demonstrate the efficiency of the CR-driven dynamo in amplifying galactic magnetic fields within a galactic rotation period.

Findings

Large-scale magnetic fields are amplified on galactic timescales.

The magnetic field structure resembles observed X-shaped fields.

Small-scale SN magnetic fields are converted into galactic-scale fields.

Abstract

We present recent developments of global galactic-scale numerical models of the Cosmic Ray (CR) driven dynamo, which was originally proposed by Parker (1992). We conduct a series of direct CR+MHD numerical simulations of the dynamics of the interstellar medium (ISM), composed of gas, magnetic fields and CR components. We take into account CRs accelerated in randomly distributed supernova (SN) remnants, and assume that SNe deposit small-scale, randomly oriented, dipolar magnetic fields into the ISM. The amplification timescale of the large-scale magnetic field resulting from the CR-driven dynamo is comparable to the galactic rotation period. The process efficiently converts small-scale magnetic fields of SN-remnants into galactic-scale magnetic fields. The resulting magnetic field structure resembles the X-shaped magnetic fields observed in edge-on galaxies.