Observations of galaxies have long hinted that the invisible substance shaping their structure may be more complex than a single particle species. A fresh theoretical effort now suggests that dark matter consists of at least two types with different masses, each behaving in its own way under the influence of self-interactions.
Researchers at the Purple Mountain Observatory of the Chinese Academy of Sciences have developed a two-component self-interacting dark matter framework. In this picture heavier particles gradually sink toward galactic centres while lighter ones diffuse outward, a process known as mass segregation. The work, published in Science Bulletin, represents the team's second exploration of the idea.
The model seeks to reconcile two stubborn puzzles in standard cold dark matter theory. Dwarf galaxies show lower central densities than simulations predict, creating what astronomers call the cusp-core problem. At the same time, certain strong gravitational lensing events imply the existence of dense small-scale structures that single-particle models struggle to produce consistently.
By allowing the two particle populations to collide with one another in addition to feeling gravity, the researchers reproduce both features. High-resolution numerical simulations demonstrate that mass segregation can carve out the observed low-density cores in dwarf galaxies while simultaneously raising the chance of finding the compact lenses required by data.
Building on earlier results
This latest paper follows an earlier study by the same group, published in Physical Review D, that examined mass segregation specifically in dwarf galaxies. The new calculations extend the framework, offering what the authors describe as a unified account of both the cores and the lenses.
Dark matter itself remains undetected in the laboratory. Its presence is inferred entirely from gravitational effects: the way stars orbit within galaxies, the patterns of cosmic structure formation, and the bending of light around massive clusters. The standard model succeeds on the largest scales yet encounters difficulties once astronomers zoom in to the smallest.