Shock Waves of the Large-Scale Structure Formation in the Universe
  Simulations of structure formation in the Universe predict accretion shock waves at the boundaries of the large-scale structures as sheets, filaments, and clusters of galaxies. If magnetic fields are present at these shocks, particle acceleration should take place, and could contribute to the observed cosmic rays of high energies. When the radio plasma of an old invisible radio lobe is dragged into such a shock wave, the relativistic electron population will be reaccelerated and the plasma becomes radio-luminous again. Such tracers of the accretion shock waves are observed at the boundaries of some clusters of galaxies: the so-called cluster radio relics, which are large regions of diffuse radio emission, without any parent galaxy nearby. The observed properties of the cluster radio relics are naturally explained by accretion shock waves. Radio relics therefore give the first evidence for the existence of accretion shocks of the large-scale structure formation and they allow investigations of the shock properties. 
Torsten A. Ensslin (1), Peter L. Biermann (1), Ulrich Klein (2), Sven   Kohle (2) ((1) MPI fuer Radioastronomie Bonn, (2) Un...