RIVERSIDE, Calif. -- A study led by UC Riverside physicist Hai-Bo Yu suggests that a new type of dark matter could explain three astrophysical puzzles across vastly different environments.
Published in Physical Review Letters , the study proposes that dense clumps of self-interacting dark matter (SIDM) — each about a million times the mass of the sun — can account for unusual gravitational effects observed in gravitational lenses, stellar streams, and satellite galaxies.
Dark matter, which makes up about 85% of the universe’s matter, cannot be seen directly. The standard model assumes it is “cold” and collisionless, meaning particles pass through one another without interacting. This model struggles, however, to explain certain high-density structures observed in the universe.
Yu’s work instead focuses on SIDM, in which dark matter particles collide and exchange energy. These interactions can trigger “gravothermal collapse,” forming extremely dense, compact cores.
“The difference is like a crowd of people who ignore each other versus one where everyone is constantly bumping into one another,” said Yu, a professor of physics and astronomy and deputy director of the Center for Experimental Cosmology and Instrumentation , to explain dark matter particles in the standard model and SIDM. “In SIDM, these interactions can dramatically reshape the internal structure of dark matter halos. Dark matter that interacts with itself can become dense enough to explain these observations.”
The study shows that these dense SIDM clumps can simultaneously explain:
“What’s striking is that the same mechanism works in three completely different settings — across the distant universe, within our galaxy, and in a neighboring satellite galaxy,” Yu said. “All show densities that are difficult to reconcile with standard model dark matter but arise naturally in SIDM.”
The research was supported by the John Templeton Foundation and the U.S. Department of Energy.
The title of the paper is “Core-Collapsed SIDM Halos as the Common Origin of Dense Perturbers in Lenses, Streams, and Satellites.”
The University of California, Riverside is a doctoral research university, a living laboratory for groundbreaking exploration of issues critical to Inland Southern California, the state and communities around the world. Reflecting California's diverse culture, UCR's enrollment is more than 26,000 students. The campus opened a medical school in 2013 and has reached the heart of the Coachella Valley by way of the UCR Palm Desert Center. The campus has an annual impact of more than $2.7 billion on the U.S. economy. To learn more, visit www.ucr.edu .
Physical Review Letters
Data/statistical analysis
Not applicable
Core-Collapsed SIDM Halos as the Common Origin of Dense Perturbers in Lenses, Streams, and Satellites
9-Apr-2026