The Self-Control of Cosmic Rays

Pasquale Blasi

doi:10.3390/galaxies7020064

Abstract

Several independent pieces of information have recently hinted at a prominent role of cosmic rays in controlling their own transport, within and around the sources as well as throughout their propagation on Galactic scales and even possibly during their escape from the Galaxy. I will discuss this topic with special attention to the theoretical implications and possible additional observational evidence that we may seek with upcoming experiments.

Highlights

The bulk of cosmic rays (CRs) is made of fully ionized light nuclei, moving at speeds close to the speed of light
It has been argued that the reacceleration scenario might run into energetic problems [9] and the steep energy dependence of the diffusion coefficient should result in excessive large scale anisotropy [10,11]
CR diffusion is often described in phenomenological terms by introducing a diffusion coefficient

Summary

Introduction

The bulk of cosmic rays (CRs) is made of fully ionized light nuclei, moving at speeds close to the speed of light. One of the most interesting topics in this context is the self-controlling action of CRs, namely their role in changing the environment in which they propagate, both inside the acceleration region and during Galactic transport, so that the diffusive properties are no longer independent of CRs themselves but rather determined by them This interaction is mediated by the excitation of plasma instabilities associated with the current of CRs that develops in any situation in which CRs are not homogeneously distributed in space (which reflects in local anisotropy). The paper is organized as follows: In Section 2, I will emphasize the effects of the excitation of streaming instability on Galactic scales, as due to the global gradient of CRs escaping the Galaxy

Nonlinear Effects in CR Galactic Transport

From Accelerated Particles to CRs

Escape from the Galaxy

Conclusions