Dark matter is invisible, but its gravity governs the motion of galaxies. What it's made of is a mystery. One idea: it consists of ultra-light particles akin to axions. Under ordinary conditions, they barely interact, but in the presence of electromagnetic radiation, they can decay into two photons, like a match that only ignites when exposed to an already burning flame.
The authors of the new study propose to catch such radio emission from dark matter using the future SKA radio telescope (Square Kilometre Array). They built a model that accounts for both the relic background and extragalactic radio noise. Then they overlaid the expected signal map onto the galaxy distribution from the 2MRS catalog in the nearby Universe. Matching patterns, radio emission spikes and galaxy clumps, would provide evidence that dark matter indeed consists of axion-like particles with masses on the order of micro-electronvolts.
Calculations show that the cross-correlation method, comparing two sky maps, can extract a weak signal from the noise. If these particles exist, the radio sky will whisper where galaxies abound. Then, for the first time, the invisible mass will become audible.
Axions are named after a brand of laundry detergent because they were supposed to 'clean up' a problem in particle physics.
In the novel 'Darkness at the Edge of the World', dark matter turns out to be a network of intelligent particles communicating via radio bursts.