Electromagnetic thermal instability with momentum and energy exchange between electrons and ions in galaxy clusters

TL;DR

This paper investigates electromagnetic thermal instability in a magnetized electron-ion plasma with separate electron and ion dynamics, including energy exchange, and derives a new dispersion relation relevant for astrophysical plasmas.

Contribution

It introduces a multicomponent plasma approach considering separate species dynamics with energy exchange, deriving a new dispersion relation for thermal instability.

Findings

Perturbations are electromagnetic in nature.

Electric field perturbations along magnetic field are crucial.

Condensation occurs along magnetic field lines.

Abstract

Thermal instability in an electron-ion magnetized plasma, which is relevant in the intragalactic medium (IGM) of galaxy clusters, solar corona, and other two-component plasma objects is investigated. We apply the multicomponent plasma approach when the dynamics of all species is considered separately through the electric field perturbations. General expressions for the dynamical variables obtained in this paper can be applied for a wide range of astrophysical and laboratory plasmas also containing neutrals and dust grains. We assume that background temperatures of electrons and ions are different and include the energy exchange in the thermal equations for the electrons and ions along with the collisional momentum exchange in the equations of motion. We take into account the dependence of collision frequency on the density and temperature perturbations. The cooling-heating functions are taken for both electrons and ions. A condensation mode of thermal instability has been studied in the fast sound speed limit. A new dispersion relation including the different electron and ion cooling-heating functions and other effects mentioned above has been derived and its simple solutions for growth rates in the limiting cases have been found. We have shown that the perturbations have an electromagnetic nature. The crucial role of the electric field perturbation along the background magnetic field in the fast sound speed limit has been demonstrated. We have found that at conditions under consideration, the condensation must occur along the magnetic field while the transverse scale sizes can be both larger and smaller than the longitudinal ones. The results obtained can be useful for interpretation of observations of dense cold regions in astrophysical objects.