Beyond MHD in Galaxy Clusters

Abstract

We demonstrate that the intracluster medium (ICM) of clusters of galaxies is everywhere convectively unstable to one of two instabilities driven by anisotropic thermal conduction along magnetic field lines, despite having stably stratified entropy gradients. Outside any cooling core, the magnetothermal instability (MTI) reorients magnetic fields to be largely radial, enhancing the effective radial thermal conductivity. In galaxy clusters with a cooling core, the heat‐flux‐driven buoyancy instability (HBI) has the opposite effect. By reducing the effective radialB thermal conductivity, the HBI can hasten the onset of a cooling catastrophe for low central entropy clusters.