Plasma physics of the intracluster medium

TL;DR

This paper reviews plasma physics principles relevant to the intracluster medium, focusing on thermal plasma dynamics, magnetic field amplification, cosmic ray processes, and observational constraints, highlighting future prospects for galaxy clusters as plasma physics laboratories.

Contribution

It provides a comprehensive tutorial on plasma physics aspects of the ICM, integrating observational data and emphasizing future research directions.

Findings

Magnetic fields in the ICM can be amplified via turbulence.

Radio observations constrain cosmic ray acceleration mechanisms.

Future X-ray and radio missions will deepen understanding of plasma processes.

Abstract

This Chapter provides a brief tutorial on some aspects of plasma physics that are fundamental to understanding the dynamics and energetics of the intracluster medium (ICM). The tutorial is split into two parts: one that focuses on the thermal plasma component -- its stability, viscosity, conductivity, and ability to amplify magnetic fields to dynamical strengths via turbulence and other plasma processes; and one that focuses on the non-thermal population of charged particles known as cosmic rays -- their acceleration, re-acceleration, and transport throughout the cluster volume. Observational context is woven throughout the narrative, from constraints on the strength and geometry of intracluster magnetic fields and the effective viscosity of the ICM, to examples of radio halos, radio relics, and cluster shocks that can test theories of particle acceleration. The promise of future X-ray missions to probe intracluster turbulence and discover the impact of small-scale plasma physics, coupled with sensitive, high-resolution radio observations of synchrotron-emitting plasma that reveal the properties of intracluster magnetic fields and particle-acceleration mechanisms, are likely to establish galaxy clusters as the premier cosmic laboratories for deciphering the fundamental physics of hot, dilute plasmas.