The sun could be a net for dark matter, a new study suggests. If dark matter happens to take a certain specific form, it could build up in our nearest star and alter how heat moves inside it in a way that would be observable from Earth.

Dark matter is the mysterious stuff that makes up about 83 percent of the matter in the universe, but doesn’t interact with electromagnetic forces. Although the universe contains five times as much dark matter as normal matter, dark matter is completely invisible both to human eyes and every kind of telescope ever devised. Physicists only know it’s there because of its gravitational effect on normal matter. Dark matter keeps galaxies spinning quickly without flying apart and is responsible for much of the large-scale structure in the universe.

Current dark matter detectors are looking for WIMPs, or weakly interacting massive particles, that connect only with the weak nuclear force and gravity. Based on the most widely accepted theories, most experiments are tuned to look for a particle that is about 100 times more massive than a proton. The chief suspect is also its own antiparticle: Whenever a WIMP meets another WIMP, they annihilate each other.

“This is something that has always worried me,” said astroparticle physicist Subir Sarkar of the University of Oxford. If equal amounts of matter and antimatter were created in the big bang, the particles should have completely wiped each other out by now. “Obviously that did not happen, we are here to prove it,” he said. “So something created an asymmetry of matter over antimatter,” letting a little bit of matter survive after all the antimatter was gone.

Whatever made regular matter beat out regular antimatter could have worked on dark matter as well, Sarkar suggests. If dark matter evolved similarly to regular matter, it would have to be much lighter than current experiments expect, only about 5 times the mass of a proton. That’s a suggestive number, Sarkar says.

“If it were five times heavier, it would get five times the abundance. That’s what dark matter is,” he said. “That’s the simplest explanation for dark matter in my view.”

The trouble is, these light particles are much more difficult to detect with current experiments. In a paper in the July 2 Physical Review Letters, Sarkar and Oxford colleague Mads Frandsen suggest another way to find light dark matter: Look to the sun.

Because lightweight dark matter particles wouldn’t vaporize each other when they meet, the sun should collect the particles the way snowballs collect more snow.

“The sun has been whizzing around the galaxy for 5 billion years, sweeping up all the dark matter as it goes,” Sarkar said.

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