A new study indicates that dark matter in the “El Gordo” galaxy cluster exhibits collisional properties, challenging the standard model of collisionless dark matter.
Contrary to what is established by the standard model, dark matter may indeed be self-interacting. This was the conclusion of a new piece of research conducted by Riccardo Valdarnini of SISSA’s Astrophysics and Cosmology group and published in Astronomy & Astrophysics (A&A).
Using numerical simulations, the study analyzed what happens inside “El Gordo” (literally “The Fat One” in Spanish), a giant cluster merger seven billion light years away from us. The calculations indicated that in this cluster the observed physical separation between the points of maximum density of dark matter and those of the other mass components can be explained using the so-called SIDM (Self-Interacting Dark Matter) model, as opposed to the standard one.
This research makes an important contribution in favor of the SIDM model, according to which dark matter particles exchange energy through collisions, with interesting astrophysical repercussions.
“El Gordo”: a gigantic cosmic structure for the study of dark matter
“According to the currently accepted standard cosmological model, the present baryonic matter density of the Universe can account for only 10% of its total matter content. The remaining 90% is in the form of Dark Matter,” explains Riccardo Valdarnini, author of the research.
“It is generally thought that this matter is nonbaryonic and made of cold collisionless particles, which respond only to gravity. Hence the name “Cold Dark Matter” (CDM). However, there are still a number of observations that have not yet been explained using the standard model,” says the researcher. “To answer these questions, several authors suggest an alternative model, called SIDM.”
Proving the collisional properties of dark matter and, more generally, alternative theories to the standard cosmological model one is very complicated: “There are, however, unique laboratories that can prove very useful for this purpose, many light years away from us. These are the massive galaxy clusters, gigantic cosmic structures that, upon collision, determine the most energetic events since the DOI: 10.1051/0004-6361/202348000