The influence of cosmic-rays on the magnetorotational instability

TL;DR

This paper investigates how cosmic rays influence the magnetorotational instability in accretion disks, revealing that cosmic rays can enhance instability growth rates, but increased diffusion diminishes this effect.

Contribution

It provides a linear perturbation analysis incorporating cosmic rays as a fluid, highlighting their destabilizing role and the impact of diffusion on the instability.

Findings

Cosmic rays increase the growth rate of the MRI.

Higher cosmic ray diffusion reduces the growth rate.

Cosmic rays have a destabilizing effect on accretion disk instabilities.

Abstract

We present a linear perturbation analysis of the magnetorotational instability in the presence of the cosmic rays. Dynamical effects of the cosmic rays are considered by a fluid description and the diffusion of cosmic rays is only along the magnetic field lines. We show an enhancement in the growth rate of the unstable mode because of the existence of cosmic rays. But as the diffusion of cosmic rays increases, we see that the growth rate decreases. Thus, cosmic rays have a destabilizing role in the magnetorotational instability of the accretion discs.