A new study led by researchers at the University of California, Riverside, suggests that a different type of dark matter could explain several puzzling cosmic observations that have long challenged scientists.
The research points to dense clumps of self-interacting dark matter as a single mechanism behind unusual structures seen across the universe.
Dark matter makes up about 85% of all matter in the universe, yet it cannot be directly observed.
The prevailing model treats it as cold and collisionless, meaning its particles pass through each other without interaction.
While this framework works well on large scales, it struggles to explain certain dense and compact structures.
The new work focuses on self-interacting dark matter, or SIDM, where particles collide and exchange energy.
These interactions can trigger a process known as gravothermal collapse, forming tightly packed cores with extremely high densities.
Each of these dense clumps can reach masses around a million times that of the Sun.
According to the study, such objects could be responsible for a range of unexplained gravitational effects observed in different parts of the cosmos.
One idea, three mysteries
“The difference is like a crowd of people who ignore each other versus one where everyone is constantly bumping into one another,” said Hai-Bo Yu.
“In SIDM, these interactions can dramatically reshape the internal structure of dark matter halos.”
One example comes from the gravitational lens system JVAS B1938+666, where astronomers have detected a small but powerful distortion in the image of a distant galaxy.
This “pinch” suggests the presence of an unseen dense object bending light through gravity.
Another case is the GD-1 stellar stream, a long trail of stars within the Milky Way. The stream shows a gap and spur pattern, as if something invisible passed through it and disrupted its structure.
The third example involves the Fornax 6 star cluster in the Fornax satellite galaxy. Its compact structure has been difficult to explain using conventional models, but a dense dark matter clump could act as a gravitational anchor, pulling stars together.
Clumps reshape cosmic structure
“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.”
By linking these observations, the study offers a unified explanation for phenomena that previously required separate interpretations. Instead of invoking different processes for each case, SIDM provides a single framework that can account for them all.
The findings also highlight how small-scale interactions within dark matter could play a larger role in shaping cosmic structures than previously thought. If confirmed, this could lead to revisions in how scientists model the formation and evolution of galaxies.
Beyond solving specific puzzles, the work opens new avenues for testing dark matter theories. Future observations of gravitational lenses, stellar streams, and satellite galaxies could help determine whether SIDM is a better fit than the traditional model.
The study was published in the journal Physical Review Letters.