Study Suggests that Dark Matter May Have Collision-Enhancing Properties After All
Contrary to what the Standard Model claims, dark matter may in fact be self-interacting. This is the result of a new study published in the journal Astronomy & Astrophysics (A&A) and carried out by Riccardo Valdarnini from the Astrophysics and Cosmology group at SISSA. The study used numerical simulations to analyze what is happening inside “El Gordo” (literally “the fat man” in Spanish), a massive star cluster located 7 billion light-years from us. The calculations showed that the physical separation between the points of maximum density of dark matter and the points of other mass components observed in this cluster can be explained by the so-called SIDM model (self-interacting dark matter), in contrast to the Standard Model. model. This work makes an important contribution to the SIDM model, in which dark matter particles exchange energy through collisions, and has interesting astrophysical implications. Unlike the Standard Model, dark matter may indeed interact with itself. This is the conclusion of a new study published in Astronomy & Astrophysics (A&A) and carried out by Riccardo Valdarnini of the Astrophysics and Cosmology group at SISSA. The study used numerical simulations to analyze what is happening inside the massive galaxy cluster “El Gordo” (Spanish for “The Fat One”), which is merging 7 billion light-years away from us. The calculations showed that the physical separation between the points of maximum density of dark matter and the points of other mass components observed in this cluster cannot be explained by the Standard Model, but can be explained by the so-called SIDM model (Self-Interacting Dark Matter). The study makes an important contribution to the SIDM model, suggesting that dark matter particles exchange energy through collisions, which has interesting astrophysical implications.
“El Gordo”: a gigantic cosmic structure to study dark matter “According to the currently accepted standard model of cosmology, the current density of baryonic matter in the Universe may only be 10% of its total matter content. The remaining 90% is in the form of dark matter,” explains Riccardo Valdalgnini, author of the study. “It is generally believed that this matter is non-baryonic and consists of cold, collisionless particles that only respond to gravity, hence the name “cold dark matter” (CDM). “However, there are still many observations that the standard model cannot yet explain,” the researcher says. “To answer these questions, several authors have proposed an alternative model called SIDM. Proving the collision properties of dark matter, as well as a more general alternative theory to the Standard Model of Cosmology, is very complicated. However, there are unique laboratories dedicated to this purpose. “Many light years away from us, they have proven to be very useful. These are gigantic clusters of galaxies, gigantic cosmic structures whose collisions would determine the most energetic events since the Big Bang. With a mass of about 1015 solar masses, El Gordo is one of the largest clusters of galaxies we know. Due to its peculiarities, El Gordo has been the subject of numerous studies, both theoretical and observational. ” Dark matter may be associated with collisions According to the standard paradigm, during the merger of clusters, the behavior of the gas mass component associated with the collision differs from that of the other two components (galaxies and dark matter). In this scenario, the gas will dissipate part of its initial energy. This is why, after the collision, the peak of gas mass density will lag behind those of dark matter and galaxies, explains Valdarnini. With the SIDM model, however, a peculiar phenomenon should be observed, namely the physical separation of dark matter centroids â its maximum density points from those of other mass components with peculiarities that represent a true Signature of SIDM.
Observations of El Gordo “Let’s start with the observations,” explains Valdarnini. El Gordo consists of two massive subclusters, designated Northwestern (NW) and Southeast (SE). X-ray images of the El Gordo cluster show a single X-ray emission peak in the SE cluster and two faint tails extending beyond the X-ray peak. A notable feature is the position of the tops of the different mass components. In contrast to what is seen in the Barrett Cluster, another important example of a colliding cluster, the X-ray peak precedes the SE dark matter peak. Moreover, the brightest galaxy in the cluster (BCG) not only lags the X-ray peak but also appears to be spatially offset from the southeastern center of mass. Another remarkable aspect is seen in the northwestern cluster, where the peak in galaxy number density is spatially offset from the corresponding mass peak. ” According to the study, collision-induced dark matter is thought to explain the phenomenon observed in El Gordo. To explain the results and validate the SIDM model, Valdarnini used a number of so-called N-body/hydrodynamic simulations in a study published in Astronomy & Astrophysics. There, he carried out a systematic study aimed at reproducing the observational features of “El Gordo”. “The most important result of this simulation study is that the relative distances observed between the different centers of mass of the ‘El Gordo’ cluster can be naturally explained by interacting dark matter,” Valdarnini explains. “Thus, these findings provide a clear indication of the behavior of dark matter that shows collision-related properties in very high-energy cluster collisions at high redshifts.” However, a contradiction arises, as the SIDM cross section values obtained from these simulations are higher than the current upper limit, which is of the order of unity at the cluster scale. This suggests that the current SIDM model should be considered only as a low-order approximation, and that the underlying physical processes describing dark matter interactions in merging large clusters are more complex than suggested by commonly accepted approaches and can be adequately represented based on the scattering of dark matter particles. This work provides a compelling argument for the possibility of self-interacting dark matter between colliding clusters, as an alternative to the standard collisionless dark matter paradigm.”
source: https://dx.doi.org/10.1051/0004-6361/202348000