This multi-wavelength image of Abell 520 shows the aftermath of a complicated collision of galaxy clusters, some of the most massive objects in the universe. In this image, the hot gas detected by Chandra is red. Optical data from the Canada-France-Hawaii and Subaru telescopes show the starlight from the individual galaxies (yellow and orange). The location of most of the matter in the cluster (blue) was also found using these telescopes, by tracing the subtle light-bending effects on distant galaxies. This material is dominated by dark matter.