Galaxy Cluster and Supercluster DynamicsThere are several exciting topics in the area of clusters and superclusters which are being investigated.
HOT-GAS BUBBLES: Especially in cooling flow clusters, the non-thermal plasma evacuates bubbles in the hot gas. In some cases the radio emission is seen, while other bubbles are attributed to radio ``ghosts'', whose radiation at cm wavelengths has faded below detection limits.
CLUSTER HALOS: Cluster synchrotron halos have been known for decades although new examples are found only slowly. Some current thinking is that they may be related to the turbulence generated from past mergers.
RELICS: There appear to be three emerging types of sources previously called 'relics': a) those directly connected to a dying/extinct AGN ( AGN relics) b) detached pieces of old radio plasma re-energized by merger or other shocks(Phoenix sources) c) those due to large scale shocks impinging on a cluster and accelerating relativistic particles (Radio Gischt)
GIANT DOUBLE RADIO GALAXIES: With sizes above 1 Mpc, such sources often strain the energy and lifetime requirements for the parent AGN, as well as local particle acceleration efficiencies.
RADIO GALAXY MOTION SHOCKS: These unusual features are found near radio galaxies, but not apparently part of the outflow from the nucleus. They may be ``triggered'' by the motion of the radio plasma or parent galaxy through the surrounding medium. The origin of the relativistic particles is unclear.
LARGE-SCALE STRUCTURES On scales of >5-10 Mpc, there is the speculative but exciting possibility of seeing shocks associated with cosmic structure formation. Many of these shocks are strong, and should accelerate cosmic rays, although a major uncertainty is the origin of the magnetic fields. There are already some encouraging hints that extended non-thermal emissions may trace larger scale structures with only conversion of shock energy into cosmic rays.