What gravitational waves have told us about the universe so far

With 90 detections now under our belt, gravitational waves are solving riddles about the evolution of galaxies and missing black holes – and they could soon give us a glimpse of dark matter

By Stuart Clark

IN A darkened room in Sweden, beneath a chandelier and surrounded by dozens of gilt-framed portraits, journalists are listening as a phone connection is established with Rainer Weiss. It is October 2017 and Weiss has just been awarded the Nobel prize in physics for spearheading the detection of gravitational waves, along with Kip Thorne and Barry Barish. The pomp and ceremony was a fitting finale to the quest to detect these elusive waves, which had been predicted by Albert Einstein more than 100 years earlier.

In truth, though, it was as much a beginning as an ending. If the traditional astronomy of telescopes is like seeing the cosmos, then gravitational wave astronomy is akin to hearing it. The discovery of these ripples in space-time had effectively given astronomers a new sense. In that room crowded with reporters, a journalist from Swedish television took the mic and asked Weiss what kind of things we might be able to learn. “Well,” he began, “there’s a huge amount of things to find out.”

Less than five years later, and with scores of gravitational waves now detected, we are starting to see what he meant. These waves are providing us with a rich picture of the universe’s most exotic objects, showing us fresh details of how stars die and explaining long-standing mysteries about the cosmic population of black holes. What’s more, we seem to be on the cusp of detecting a whole new kind of gravitational wave, one that could tune us in to the frequency of some deeply mysterious objects we think were forged in the aftermath of the big bang.

Giant …