Researchers at the Perimeter Institute have created a new computational tool to model self-interacting dark matter, addressing a gap in previous simulations. This innovation allows for faster and more accurate studies of how such dark matter influences galaxy formation. The work, published in Physical Review Letters, could reveal insights into cosmic structures and black hole origins.
For nearly a century, dark matter has puzzled cosmologists due to its invisible yet gravitational role in shaping galaxies and the universe's large-scale structure. In a study published in Physical Review Letters, James Gurian, a postdoctoral fellow at the Perimeter Institute, and Simon May, now an ERC Preparative Fellow at Bielefeld University, introduce KISS-SIDM, a new code to simulate self-interacting dark matter (SIDM).
SIDM consists of particles that collide elastically with each other but not with ordinary baryonic matter. These interactions can drive gravothermal collapse in dark matter halos—vast clumps surrounding galaxies that are denser than the universe's average but relatively diffuse. "Dark matter forms relatively diffuse clumps which are still much denser than the average density of the universe," Gurian explains. "The Milky Way and other galaxies live in these dark matter halos."
The process involves energy transport: self-interactions move energy outward, heating and densifying the halo's core. "You have this self-interacting dark matter which transports energy, and it tends to transport energy outwards in these halos," Gurian says. "This leads to the inner core getting really hot and dense as energy is transported outwards." Over time, this may culminate in core collapse, potentially linked to black hole formation.
Prior simulations fell short in the intermediate regime between sparse, infrequent collisions (handled by N-body methods) and dense, frequent ones (suited to fluid models). "But for the in-between, there wasn't a good method," Gurian notes. KISS-SIDM bridges this gap, offering precision with minimal computational demands—it runs on a laptop and is publicly available.
"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," Gurian adds. The tool gains relevance from recent galaxy observations suggesting anomalies that standard dark matter models cannot explain.
Neal Dalal, a Perimeter Institute faculty member, praises the advance: "Their paper should enable a broad spectrum of studies that previously were intractable." Yet questions persist, such as the collapse's endpoint. "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," Gurian says.
This development opens doors to probing dark matter's role in cosmic evolution, potentially reshaping understandings of galaxies and black holes.