Influence of energy exchange of electrons and ions on the long-wavelength thermal instability in magnetized astrophysical objects

TL;DR

This paper develops a multicomponent plasma model to analyze long-wavelength thermal instability in magnetized astrophysical objects, considering separate electron and ion dynamics, energy exchange, and electromagnetic effects, revealing conditions for filament formation.

Contribution

It introduces a general dispersion relation for thermal instability in multicomponent plasmas with separate electron and ion dynamics, including energy exchange and electromagnetic effects.

Findings

Perturbations are electromagnetic in nature.

Unstable perturbations can form very thin filaments.

The model applies to various astrophysical and laboratory plasmas.

Abstract

We investigate thermal instability in an electron-ion magnetized plasma relevant to galaxy clusters, solar corona, and other two-component astrophysical objects. We apply the multicomponent plasma approach when the dynamics of all the species are considered separately through electric field perturbations. General expressions for perturbations obtained in this paper can be applied for a wide range of multicomponent astrophysical and laboratory plasmas also containing the neutrals, dust grains, and other species. We assume that background temperatures of electrons and ions are different and include the energy exchange in thermal equations. We take into account the dependence of collision frequency on density and temperature perturbations. The cooling-heating functions are taken as different ones for electrons and ions. As a specific case, we consider a condensation mode of thermal instability of long-wavelength perturbations when the dynamical time is smaller than a time during which the particles cover the wavelength along the magnetic field due to thermal velocity. We derive a general dispersion relation taking into account the effects mentioned above and obtain simple expressions for growth rates in limiting cases. Perturbations are shown to have an electromagnetic nature. We find that at conditions under consideration transverse scale sizes of unstable perturbations can have a wide spectrum relatively to longitudinal scale sizes and, in particular, form very thin filaments. The results obtained can be useful for interpretation of observations of dense cold regions in astrophysical objects.