Scientists from the International School of Advanced Studies in Italy believe that dark matter may be a self-interacting substance.
Scientists reached this conclusion regardless of the prevailing view that dark matter consists of cold particles that never collide with anything and do not interact and respond only to gravity. Scientists published the results of their study in the journal "Astronomy and Astrophysics."
Using computer simulations, the researchers analyzed what is happening inside El Gordo ("the fat man" in Spanish), a giant cluster of galaxies seven billion light-years from Earth.
Calculations showed that the generally accepted standard model of physics does not explain the difference observed in this group between the maximum density points of dark matter and its other massive components, but can be explained by the so-called SIDM (self-interacting dark matter) model, according to which dark matter particles exchange energy. Through collisions.
Riccardo Valdarnini, who led the study, explained: “There is a widespread belief that dark matter consists of cold particles that never collide with anything and do not interact and respond only to gravity. However, there are a number of observations and discoveries that have not been explained with the help of the Standard Model.”
Proving the "collision" properties of dark matter and SIDM theory is extremely difficult. However, at a distance of many light-years from us, there are unique "laboratories" that can be very useful for this purpose - huge accumulations of galaxies with a mass of about 10-15 solar masses, and El Gordo is one of the largest of these clusters. known.
According to the Standard Model, when clusters of galaxies merge, the gas that makes up part of the total mass will behave differently from other components, namely dark matter and the relatively dense structures of the galaxies themselves. The gas will dissipate part of its initial energy. For this reason, after the collision, the denser regions of gas will be smaller compared to the denser regions of dark matter and galaxies.
The El Gordo galaxy cluster consists of two huge subclusters, the northwest group and the southeast group. It turns out that the peak of X-ray radiation in the Southeast Cluster, which in galaxy clusters is associated with hot galactic gas, is larger in observations than the dark matter peak. The center of dark matter density in the Northwest Cluster is shifted relative to the center of mass. In the Northwest Cluster, the highest density of galaxies is not located in the center of the cluster.
Computer simulations showed that the current situation could only be explained if dark matter interacted with itself.
However, there are also inconsistencies even in the SIDM model where dark matter activity is higher than assumed by this theory.
This suggests that current SIDM models should be considered only approximations, and that the fundamental physical processes describing dark matter interactions in large cluster mergers are more complex than can be adequately represented by an approach based on dark matter particle scattering.
Nice discovery.
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