English: Cluster Collisions Switch on Radio Halos This is a composite image of the northern part of the galaxy cluster Abell 1758 showing the effects of a collision between two smaller galaxy clusters. Chandra X-ray data (blue) reveal hot gas in the cluster and data from the Giant Metrewave Radio Telescope (GMRT) in India (pink) shows huge "halos" generated by ultra-relativistic particles and magnetic fields over vast scales. Optical data from the Digitized Sky Survey are colored gold. A study of this galaxy cluster and 31 others with Chandra and the GMRT shows that huge radio halos are generated during collisions between galaxy clusters.