Dark matter is the invisible scaffolding of the universe. It's there, we know from the motion of stars and galaxies, but what this scaffolding is made of remains unknown. One guess is ultra-light particles similar to axions. They barely interact with ordinary matter, yet occasionally they do get involved.
The authors built a model: inside dark matter halos, these invisible particles collide with protons of cosmic rays. Cosmic rays are particles accelerated by supernova explosions. The impact produces gamma-ray emission — the most energetic light. Telescopes can catch it, but the signal is faint and smeared across the sky. To pick it out from the background, the scientists propose cross-referencing the gamma-ray glow map from the Fermi satellite with the 2MRS catalog of nearby galaxies. If the glow is slightly brighter where there are more galaxies, that's a clue.
Such cross-analysis opens a new avenue for dark matter searches. No need to catch the particles themselves, just spot their shadow on the cosmic background. The method promises to probe corners of theory previously out of reach, and perhaps finally hear the voice of the invisible scaffolding.
The most energetic gamma rays produced in such collisions can be a trillion times more energetic than visible light.