Radio sources and the evolution of the intracluster medium

The energy available from active galactic nuclei and their accompanying radio sources in clusters of galaxies have been suggested as energy sources that can solve the "cooling flow problem" in rich clusters of galaxies. In particular, fragmentation and subsequent mixing of buoyant radio source bubbles and relics has been proposed as a mechanism for mixing and reheating the intracluster medium. However, inclusion of the effects of the magnetic field present in the ICM of most clusters shows that the situation is more complex than might have been thought. Using self consistent 2-D and 3-D MHD calculations of the evolution of radio source bubbles in clusters, including their formation and including both galaxy and cluster gravitational potentials, it is shown that the buoyant bubbles are stable against fragmentation over times comparable to their buoyant risetimes and to the cooling times in clusters. In addition, lifting and mixing of the ICM is confined to volumes directly below the rising bubble and thus does not include an appreciable fraction of the overall volume of the ICM in the inner regions of clusters. Hence some additional mixing and fragmentation mechanisms may be required in order to effectively use radio sources in clusters as a means of general reheating of the ICM on times comparable in inner cluster cooling times.