Scientists may be closer to observing dark matter, a substance theorized to make up about 85 percent of the universe’s matter, thanks to a new study proposing a self-interacting form of the invisible material. While dark matter’s gravitational effects are detectable, its elusive nature has made direct observation difficult for centuries.
Most prevailing theories describe dark matter as “collisionless” and “cold,” meaning its particles interact minimally with each other and other matter, and move slowly. However, research published in Physical Review Letters suggests a different model: self-interacting dark matter. In this scenario, the particles would actively interact with each other and their surroundings.
Hai-Bo Yu, a physicist at the University of California, Riverside, and a co-author of the study, likens self-interacting dark matter particles to people in a crowd who bump into each other, rather than passively avoiding one another. This interaction, Yu suggests, could help explain the formation of certain structures observed in the universe.
Explaining Cosmic Mysteries
The hypothesis that dark matter might interact with itself could offer explanations for several observed cosmic phenomena that are difficult to account for with current models. One challenge in verifying these theories, according to Yonatan Khan, a physicist at the University of Toronto who was not involved in the study, is the fundamental lack of knowledge about dark matter’s composition, mass, and interaction forces.
Yu proposes that when self-interacting dark matter particles collide, they generate immense energy, potentially creating dense, compact cores. While current particle colliders are not yet powerful enough to detect these specific particles, the existence of such cores, if found, could help resolve three significant cosmic puzzles.
Stellar Streams and Gravitational Lenses
One such puzzle involves GD-1, a stream of stars approximately 25 light-years away, which appears “scarred.” A 2025 paper co-authored by Yu suggested that an object with the density and self-interacting nature of dark matter would be required to create such a large scar, exceeding the explanatory power of cold dark matter. Further observations of stellar streams, potentially enabled by new wide-field telescopes like the Vera C. Rubin Observatory coming online in the next five years, could help differentiate between this theory and other explanations, such as changes in a galaxy’s gravitational field over time.
Self-interacting dark matter may also shed light on gravitational lenses, phenomena where dense objects magnify light from background objects. Yu points to an ultra-dense dark matter object potentially contributing to the gravitational lens system JVAS B1938+666. However, confirming this is challenging due to the distance and the possibility of multiple contributing factors, including the gravity of nearby galaxies.
Unusual Star Clusters
Another area of investigation is the Fornax satellite galaxy, which hosts an unusual star cluster known as Fornax 6. This cluster is dimmer and irregularly shaped compared to expectations. While some attribute this to gravitational influence from its host galaxy, Yu suggests that a clump of dark matter might be trapping stars within the cluster. As with other aspects of this theory, new observatories will be crucial for gathering more evidence and validating these ideas.
Both Yu and Khan agree that accumulating more data could solidify the role of self-interacting dark matter in explaining these cosmic anomalies and potentially reveal more about the fundamental nature of the universe.
Helene Elliott is the senior reporter for News Raise. She covers Science news. She also has a keen interest in photojournalism. Helene holds a nomination for the prestigious Red Smith Award. She is married to author Dennis D’Agostino, a former publicist with the New York Mets.
