A new type of self-interacting dark matter could provide solutions to three very different cosmic puzzles, new research suggests.
First, the research addresses an ultradense clump of matter detected in the system JVAS B1938+666, which is gravitationally lensed due to a phenomenon explained by general relativity. The second puzzle concerns a visible « scar » in a stellar stream known as GD-1, which appears as though a dense, invisible object has disrupted the stream. Lastly, the formation of an unusual star cluster named Fornax 6 in the Fornax satellite galaxy of the Milky Way may be explained by a dense patch of dark matter acting as a gravitational trap for passing stars.
Research indicates that if dark matter interacts with itself, it could clarify all three phenomena. « 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, » said Hai-Bo Yu from the University of California, Riverside. He emphasized that these scenarios exhibit densities challenging to reconcile with standard model dark matter but arise naturally in self-interacting dark matter.
Dark matter constitutes approximately 85% of the universe’s matter, significantly outweighing ordinary matter, which includes stars, planets, and moons. It is known that dark matter cannot consist of protons, electrons, and neutrons, as these particles interact with light, making dark matter effectively invisible and detectable only through its gravitational effects.
In the prevailing model of cosmology, known as lambda cold dark matter (LCDM), dark matter is considered « cold, » meaning its particles move slowly and do not collide, passing through one another without interaction. In contrast, self-interacting dark matter allows for collisions between particles, leading to energy and momentum exchange. This can result in « gravothermal collapse, » forming dense, compact cores of dark matter.
Yu illustrated this concept by comparing self-interacting dark matter to a crowd where individuals constantly bump into each other, reshaping the internal structure of dark matter halos. « Dark matter that interacts with itself can become dense enough to explain these observations, » he concluded.
The findings of this study were published on April 9 in the journal Physical Review Letters.
