This image is from a computer simulation of the distribution of matter in the universe. Orange regions host galaxies; blue structures are gas and dark matter. We can map dark matter, but we don't know what it is. Image Credit: TNG Collaboration
Proving that dark matter can interact with itself via collisions is difficult and complicated. El Gordo is a good place to study the Self-Interacting Dark Matter idea. “There are, however, unique Observations of El Gordo show that it consists of two large sub-clusters, the northwest and the southeast , which are merging into one.
This combined X-ray and infrared image shows X-rays from Chandra in pink, and the blue shows where dark matter is found. Image Credit: X-ray: NASA/CXC/Rutgers/J. Hughes et al.; Infrared: NASA/ESA/CSA, J.M. Diego , B.Frye , P.Kamieneski, T.Carleton & R.Windhorst “The most significant result of this simulation study is that the relative separations observed between the different mass centroids of the “El Gordo” cluster are naturally explained if the dark matter is self-interacting,” states Valdarnini.