Researchers at Perimeter Institute are now delving deeper into how a specific dark matter candidate, known as self-interacting dark matter (SIDM), might shape the evolution of cosmic structures. The study was published in Physical Review Letters.
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For nearly a century, the enigmatic nature of dark matter and its profound influence on cosmology have captivated physicists.
James Gurian and Simon May introduced a novel computational code. This code is designed to investigate the intricate relationship between SIDM and galactic evolution, opening avenues for research into a spectrum of particle interactions previously beyond the reach of existing methodologies.
Dark Matter That Dances Alone
SIDM particles are theorized to possess the unique ability to collide and interact with each other, yet remain aloof from baryonic matter, the observable "ordinary" matter composed of protons, neutrons, and electrons. These SIDM collisions are elastic, meaning they conserve energy. This characteristic has significant implications for dark matter halos, the theoretical structures believed to be pivotal in the processes of star formation and galaxy evolution.
Dark matter forms relatively diffuse clumps, which are still much denser than the average density of the universe. The Milky Way and other galaxies live in these dark matter halos.
James Gurian, Postdoctoral Fellow and Study Co-Author, Perimeter Institute
The nature of Self-Interacting Dark Matter (SIDM) drives a process known as gravothermal collapse within these dark matter halos. Gravothermal collapse arises from the counterintuitive principle that gravitationally-bound systems become hotter when energy is removed, rather than cooling.
“You have this self-interacting dark matter which transports energy, and it tends to transport energy outwards in these halos. This leads to the inner core getting really hot and dense as energy is transported outwards,” said Gurian.
The endgame of this process is a gravothermal core collapse.
Mapping the structures formed by SIDM presents a challenge, but physicists have developed several approaches, each optimized for specific matter densities.
“One approach is an N-body simulation approach that works really well when dark matter is not very dense, and collisions are infrequent. The other approach is a fluid approach, and this works when dark matter is very dense, and collisions are frequent. But for the in-between, there wasn’t a good method. You need an intermediate range approach to correctly go between the low-density and high-density parts. That was the origin of this project,” said Gurian.
Gurian and co-author Simon May, a former Perimeter postdoctoral researcher and now ERC Preparative Fellow at Bielefeld University, developed a code to address this gap. The code, KISS-SIDM, offers improved speed and accuracy compared to previous codes and is publicly accessible to researchers.
“Before, if you wanted to check different parameters for self-interacting dark matter, you needed to either use this really simplified fluid model or go to a cluster, which is computationally expensive. This code is faster, and you can run it on your laptop,” said Gurian.
There has been considerable interest recently in interacting dark matter models, due to possible anomalies detected in observations of galaxies that may require new physics in the dark sector.
Neal Dalal, Research Faculty, Perimeter Institute
“Previously, it was not possible to perform accurate calculations of cosmic structure formation in these sorts of models, but the method developed by James and Simon provides a solution that finally allows us to simulate the evolution of dark matter in models with significant interactions. Their paper should enable a broad spectrum of studies that previously were intractable,” said Dalal.
Physicists are also interested in understanding the core collapse process due to its potential observable implications for black hole formation. However, the precise details of how this process concludes remain an open question in physics, according to Gurian. He states that this code represents a step towards answering that question.
“The fundamental question is, what’s the final endpoint of this collapse? That’s what we’d really like to do -- study the phase after you form a black hole,” said Dalal.
Journal Reference:
Gurian, J. and May, S. (2025) Core Collapse Beyond the Fluid Approximation: The Late Evolution of Self-Interacting Dark Matter Halos. Physical Review Letters. DOI: 10.1103/2ycz-3fvv. https://journals.aps.org/prl/abstract/10.1103/2ycz-3fvv