This picture depicts dark clouds - Galaxies and galaxy clusters are surrounded by dark matter (illustrated in blue over an image of a cluster Abell 2744; red indicates gas). Dark matter particles may undergo a process called dark fusion as suggested by Samuel D. Mc Dermott in a recent publication in Physical Review Letters.  Assistant professor of astronomy and physics, Annika Peter, was quoted in the article in ScienceNews describing this publication and this idea of "dark fusion."  Read more.