And way beyond our galaxy, two galaxy clusters collide...
**Abell 520: Dark Matter Mystery Deepens in Cosmic "Train Wreck"
Astronomers have discovered a chaotic scene unlike any witnessed before in a cosmic "train wreck" between giant galaxy clusters. NASA's Chandra X-ray Observatory and optical telescopes revealed a dark matter core that was mostly devoid of galaxies, which may pose problems for current theories of dark matter behavior.
http://chandra.harvard.edu/photo/2007/a520/
