Astronomers studying the dawn of the universe may have made a new detection of dark matter interacting with ordinary matter.
In the four decades since its discovery, dark matter has eluded every attempt to directly detect it. It doesn’t interact with light or regular matter, so the only way astronomers have been able to infer its presence is in how its gravity tugs on regular matter.
But when the universe first went from dark to light, 180 million years after the Big Bang, the particles in the cold gas throughout the universe seem to have bumped up against their dark-matter cousins, according to new research published in Nature on Wednesday. It’s the first sign that dark matter interacts with regular matter through anything other than gravity.
“Finding this minuscule signal has opened a new window on the early universe,” lead author Judd Bowman of Arizona State University told The Guardian.
The discoverers, led by Bowman, originally set out to find what’s known as “cosmic dawn”: the moment in time when the first stars flicked on. Any light these stars emitted is too faint for ordinary telescopes to pick up, but in theory, the moment should be detectable in a radio signal released when light from these stars excited the cold gas around it.
For a long time, there was little hope. The signal seemed impossible to disentangle from other radio signals reaching Earth. But the milestone discovery published on Wednesday, radio astronomers using a small, table-shaped antenna in remote western Australia detected this blip in history.
As if that weren’t momentous enough, it came with a surprise: The signal was more than twice as strong as they predicted.
Their predictions were based on the temperature of the gas pervading the early universe. They knew this was the coldest point in the universe’s history: Heat from the Big Bang had faded, and the first stars had yet to heat up the gas around them. But in order for the signal to be as strong as it was, the gas must have been even colder than they predicted.
Something has to have cooled down the gas—and the most likely contender is cold dark matter. If this interpretation is correct, it reveals more than ever about what these mysterious particles may be like.
Scientists currently know little about the nature of dark matter. “We have no other positive statement about it, really, other than it exists and it’s 25% of the universe,” said Matt Buckley, a professor of astrophysics at Rutgers University who studies the particle nature of dark matter.
Buckley emphasizes the need for caution in interpreting these new results, which are based on a single observation. But if the findings are confirmed, he said, the result would be tremendously exciting. “It wouldn’t tell us what it is, but it would tell us where to start looking.”