A new cosmic stopwatch using colliding galaxy clusters has narrowed the search for what dark matter actually is.
Scientists have long struggled to measure if dark matter particles bump into each other as they pass through the void. By using the distance between shock waves in cluster collisions, researchers have created a much cleaner measurement tool. This new ruler establishes a strict limit on dark matter self-interaction that is more reliable than previous estimates. It removes the guesswork caused by the angle we are viewing the collision from or how fast it happened. This narrowed limit helps physicists rule out many incorrect theories about the most mysterious substance in the universe.
A New Robust Constraint on the Self-interaction Cross-section of Dark Matter with Double Radio Relic Clusters
arXiv · 2605.00093
Merging galaxy clusters are a promising laboratory for measuring the self-interaction cross-section (SICS) of dark matter. However, previous studies have focused on galaxy-mass offsets, which numerical simulations have shown to be intrinsically small because galaxies remain tightly coupled to the dominant dark matter potential even with significant self-interaction. Their interpretation is further complicated by unknowns of the merger phase, geometry, and initial conditions. In this paper, we ov