For the first time, scientists have observed weak waves caused by the motion of black holes, which gently stretch and compress everything in the universe. On Wednesday, they reported that they could “hear” changes in the fabric of the universe created by so-called low-frequency gravitational waves – massive objects moving and colliding in space.

“This is the first time we really have evidence of such a large-scale movement of everything in the universe,” said Maura McLaughlin, co-director of the research community NANOGrav, whose results are published in The Astrophysical Journal Letters.

Einstein predicted that when really heavy objects move through space-time—the fabric of our universe—they create ripples that propagate through this fabric. Scientists sometimes compare these fluctuations to the background music of the universe.

In 2015, scientists used the LIGO experiment for the first time to detect gravitational waves, and they showed that Einstein was right. But NANOGrav member Chiara Mingarelli, an astrophysicist at Yale University, explained that so far these methods have only been able to capture waves at high frequencies. According to Mingarelli, these rapid “chirps” occur at specific moments when relatively small black holes and dead stars collide.

In recent research, scientists have looked for waves at much lower frequencies. The up and down cycles of these slow waves can take years or even decades, and are likely caused by some of the largest objects in our universe: supermassive black holes billions of times the mass of our Sun.

Galaxies in the universe are constantly colliding and merging. Marka Szabolch, an astrophysicist at Columbia University who was not involved in the work, explained that when this happened, scientists believed that the supermassive black holes at the centers of these galaxies also began to clump together and dance, and eventually began collapsing into each other.

Black holes send gravitational waves as they spin in these pairs, known as binaries.

“Slowly and calmly orbiting each other, supermassive black hole duos are the tenors and basses of space opera,” Brand said.

No instrument on earth can catch waves from these giants. “So we had to make a detector roughly the size of a galaxy,” said NANOGrav researcher Michael Lam of the SETI Institute.

The results, published this week, included 15 years of data from NANOGrav, which uses telescopes in North America to look for waves. Other gravitational wave hunter groups around the world, including Europe, India, China and Australia, have also published research.

The scientists pointed telescopes at dead stars called pulsars, which send out radio waves as they spin through space like space beacons.

These bursts are so regular that scientists know exactly when the radio waves will reach our planet — “like a perfectly running clock in space,” said NANOGrav member Sarah Vigeland, an astrophysicist at the University of Wisconsin-Milwaukee. . But when gravitational waves bend the fabric of space-time, they actually disrupt this steady pulse by changing the distance between Earth and these pulsars.

By analyzing the small changes in the tick-tock speeds of different pulsars—with some pulses arriving a little earlier and others later—the scientists were able to determine that gravitational waves were passing through them.

Using the Green Bank Telescope in West Virginia, the Arecibo Telescope in Puerto Rico, and the Very Large Array in New Mexico, the NANOGrav team observed 68 pulsars in the sky. Other groups have found similar evidence in dozens of other pulsars observed with telescopes around the world.

Mark Kamionkowski, an astrophysicist at Johns Hopkins University who was not involved in the study, said that until now the method has not been able to track exactly where these low-frequency waves are coming from.

Instead, standing in the middle of a party brings out the constant hum that surrounds us, like, “You’ll hear all these people talking, but you won’t hear anything specific,” Kamionkowski said. .

The background noise they found is “louder” than some scientists expected, according to Mingarelli. This could mean there are more or more merging black holes in space than we thought, or it could point to other sources of gravitational waves that could challenge our understanding of the universe.

Researchers hope that continuing to study such gravitational waves will help us learn more about the largest objects in our universe. Brand said it could open new doors to “space archaeology,” which can trace the history of black holes and the merging of galaxies around us.

“We’re starting to open this new window in the universe,” Vigeland said.