Dark matter has long been one of astronomy’s greatest mysteries. It cannot be seen or touched, yet its gravitational influence helps shape galaxies and the large scale structure of the universe. For decades, scientists have relied on the “cold dark matter” model to explain how galaxies formed and evolved. But as telescopes and observations have become more precise, researchers have uncovered several puzzling features that the standard model struggles to explain.
Among the biggest mysteries are the surprisingly low concentrations of dark matter found at the centers of some dwarf galaxies and the unexpectedly dense dark matter clumps inferred from strong gravitational lensing. Although these observations seem to point in opposite directions, a new study suggests they could share the same underlying explanation.
A New Theory for Dark Matter
Physicists at the Purple Mountain Observatory of the Chinese Academy of Sciences (CAS) propose that dark matter may not consist of a single type of particle. Instead, it could be made up of particles with different masses.
Their new “two component self interacting dark matter” model includes at least two kinds of dark matter particles, one heavier and one lighter. In addition to interacting through gravity, these particles can also collide directly with one another. Those interactions lead to a process called “mass segregation.”
In simple terms, heavier dark matter particles gradually drift toward the centers of galaxies, while lighter particles spread outward over time. Researchers compare this behavior to star clusters, where the most massive stars slowly migrate inward and lower mass stars move farther from the center.
Simulations Match Cosmic Observations
Using high resolution computer simulations combined with detailed theoretical modeling, the team found that mass segregation naturally reproduces a broad range of astronomical observations.
In dwarf galaxies, the process creates dark matter cores with relatively low central densities, matching recent observations of galaxy clustering. In larger and more complex environments, some dark matter halos become increasingly compact, producing dense structures capable of generating strong gravitational lensing.
The model also boosts the likelihood of small scale gravitational lensing events. As heavier dark matter particles accumulate in key regions, dark matter substructures become more effective at magnifying the light from distant background galaxies. This could help explain why astronomers observe more small scale strong lensing events than traditional models predict.
A Richer Picture of the Invisible Universe
The researchers say these seemingly contradictory cosmological puzzles may actually point toward the same conclusion. Rather than requiring separate explanations, they could all reflect the fact that dark matter has more complex internal properties than previously thought.
As future sky surveys and gravitational lensing observations become even more precise, scientists will have new opportunities to test whether dark matter is truly made of multiple components. Those natural “cosmic magnifying glasses” could provide some of the strongest evidence yet for this new picture of the invisible universe.
The findings are the second study from the Purple Mountain Observatory team exploring two component self interacting dark matter. Their earlier work, published in Physical Review D, examined how mass segregation influences the wide range of dark matter core densities observed in dwarf galaxies. The new research was published in Science Bulletin. The study’s authors are Daneng Yang, Yi-Zhong Fan, Siyuan Hou, and Yue-Lin Sming Tsai.
Purple Mountain Observatory, part of the Chinese Academy of Sciences, is one of China’s leading centers for dark matter research. The institute plays a major role in indirect dark matter detection through the DAMPE (Wukong) satellite and conducts influential research in astrophysics, cosmology, dark matter, and galaxy evolution.