New Study Suggests Dark Matter May Be Self-Interacting

New Study Suggests Dark Matter May Be Self-Interacting
by Erica Marchand
Paris, France (SPX) Jun 01, 2024

Recent research conducted by Riccardo Valdarnini of SISSA's Astrophysics and Cosmology group challenges the standard model by suggesting that dark matter may be self-interacting. The study, published in "Astronomy and Astrophysics" (A&A), used numerical simulations to analyze the giant cluster merger "El Gordo," located seven billion light years away. The findings indicate that the physical separation between the points of maximum density of dark matter and other mass components in the cluster can be explained using the Self-Interacting Dark Matter (SIDM) model.

Riccardo Valdarnini explains, "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. It is generally thought that this matter is non baryonic 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 which have not yet been explained using the standard model."

The study highlights the importance of galaxy clusters like El Gordo in understanding dark matter. El Gordo, with a mass of about 10^15 solar masses, has been extensively studied due to its unique characteristics. Valdarnini's research suggests that during a cluster merger, the behavior of the collisional gas mass component will differ from that of galaxies and dark matter. The gas will dissipate part of its initial energy, causing the peak of gas mass density to lag behind those of dark matter and galaxies.

However, in the SIDM model, a physical separation of dark matter centroids from other mass components is expected. Observations of El Gordo support this model, as the X-ray peak in the SE subcluster precedes the SE dark matter peak, and the Brightest Cluster Galaxy (BCG) is offset from the SE mass centroid. Similar offsets are observed in the NW cluster.

Valdarnini's study used a large set of N-body/hydrodynamical simulations to reproduce these observational features. "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. He notes that these findings provide an unambiguous signature of dark matter behavior exhibiting collisional properties. However, he also acknowledges that the SIDM cross-section values obtained are higher than current upper limits, suggesting that present SIDM models are only a low-order approximation.

Research Report:An N-body/hydrodynamical simulation study of the merging cluster El Gordo: A compelling case for self-interacting dark matter?