Environments for Magnetic Field Amplification by Cosmic Rays

TL;DR

This paper investigates cosmic ray-driven instabilities that can amplify magnetic fields across various astrophysical environments, including intergalactic space and galaxies, highlighting their potential role in magnetic field evolution.

Contribution

It demonstrates that cosmic ray streaming instabilities are applicable beyond supernova shocks, influencing magnetic fields in diverse cosmic settings.

Findings

Instabilities are strongest in warm ionized gas within the Milky Way.

They can operate in intergalactic medium and weakly magnetized galaxies.

Effectiveness depends on cosmic ray injection efficiency.

Abstract

We consider a recently discovered class of instabilities, driven by cosmic ray streaming, in a variety of environments. We show that although these instabilities have been discussed primarily in the context of supernova driven interstellar shocks, they can also operate in the intergalactic medium and in galaxies with weak magnetic fields, where, as a strong source of helical magnetic fluctuations, they could contribute to the overall evolution of the magnetic field. Within the Milky Way, these instabilities are strongest in warm ionized gas, and appear to be weak in hot, low density gas unless the injection efficiency of cosmic rays is very high.