Simulations of El Gordo, one of the most massive and distant galaxy clusters ever observed, provide strong indications that dark matter could interact with itself through collisions. The study, conducted by Riccardo Valdarnini, a former researcher in SISSA’s Astrophysics and Cosmology group, shows that the observed properties of the cluster are particularly well reproduced by a two-state self-interacting dark matter model, in which particles can collide and exchange energy through both elastic and inelastic scattering channels. These findings, published in The Astrophysical Journal, offer new clues about the nature of one of the greatest mysteries in cosmology, although they will need to be tested through the study of other merging clusters. (Image from Wikipedia)