Scientists have finally “heard” the chorus of gravitational waves rippling through the universe

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This undated photo, submitted by researchers in June 2023, shows the Arecibo Telescope in Puerto Rico. This and several other telescopes around the world were used to observe the slow gravitational waves — weak waves produced by massive black holes — that are constantly stretching and compressing everything in the universe ever so slightly, as described in a report published Wednesday, June 28. 2023. Credit: NAIC via AP

For the first time, scientists have observed faint waves caused by the motion of black holes, which gently stretch and compress everything in the universe.

They reported on Wednesday that they were able to “hear” so-called low-frequency gravitational waves, changes in the structure of the universe caused by massive objects moving and colliding in space.

“It’s really the first time we have evidence of just this large-scale movement of the entire universe,” said Maura McLaughlin, co-director of NANOGrav, a research collaboration that published the results in The Astrophysical Journal Letters.

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

In 2015, scientists used an experiment called LIGO to detect gravitational waves for the first time and showed that Einstein was right. But so far, these techniques have only been able to detect waves at high frequencies, explained NANOGrav participant Chiara Mingarelli, an astrophysicist at Yale University.

These rapid “chirps” come from specific moments when relatively small black holes and dead stars crash into each other, Mingarelli said.






This illustration, provided by researchers in June 2023, shows gravitational waves stretching across the universe and compressing space and time. On Wednesday, June 28, 2023, researchers reported signals from so-called low-frequency gravitational waves, changes in the structure of the universe caused by massive objects moving and colliding in space. It took scientists around the world decades of work to track down evidence of these ultra-slow fluctuations. Credit: Aurore Simonnet / NANOGrav collaboration

In more recent research, scientists looked for waves at much lower frequencies. These slow waves can take years or even decades to travel up and down, and they probably come from some of the largest objects in our universe: supermassive black holes billions of times the mass of our sun.

Galaxies throughout the universe are constantly colliding and merging together. As this happens, scientists believe the supermassive black holes at the centers of these galaxies also coalesce and engage in a dance before finally collapsing into one another, explained Columbia University astrophysicist Szabolz Marka, who was not involved in the research.

Black holes emit gravitational waves as they orbit in these pairs, known as binaries.

“Supermassive black hole binaries orbiting each other slowly and calmly are the tenors and basses of the cosmic opera,” said Mark.






This photo provided by researchers shows the NANOGrav team meeting at the Green Bank Observatory in Green Bank, W.Va., in 2018. On Wednesday, June 28, 2023, researchers reported signals from so-called low-frequency gravitational waves, changes in the fabric of the universe caused by massive objects moving and colliding through space. It took scientists around the world decades of work to track down evidence of these ultra-slow fluctuations. Credit: NANOGrav via AP

No instruments on Earth could detect the waves of these giants. So “we had to build a detector that was about the size of a galaxy,” said NANOGrav researcher Michael Lam of the SETI Institute.

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

Scientists pointed the telescopes at dead stars called pulsars, which emit bursts of radio waves as they spin through space like beacons.

These bursts are so regular that scientists know exactly when the radio waves should reach our planet — “like a perfectly regular clock ticking far out in space,” said NANOGrav participant Sarah Vigeland, an astrophysicist at the University of Wisconsin-Milwaukee. . But as gravitational waves warp the fabric of spacetime, they actually change the distance between Earth and these pulsars, causing this steady beat.






This undated photo, submitted by researchers in June 2023, shows the Green Bank Observatory in Greenbank, W.Va. This and several other telescopes around the world were used to observe slow gravitational waves, weak waves produced by massive black holes. stretching and compressing everything in the universe, described in a report published on Wednesday, June 28, 2023. Credit: Jay Young/Green Bank Observatory via AP

By analyzing small changes in ticking rates in different pulsars—some pulses coming a little early and others coming late—scientists were able to determine that gravitational waves were passing through.

The NANOGrav team observed 68 pulsars in the sky using the Green Bank Telescope in West Virginia, the Arecibo Telescope in Puerto Rico, and the Very Large Array in New Mexico. Other teams found similar evidence from dozens of other pulsars observed by telescopes around the world.

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

Instead, it reveals the constant hum that’s all around us, like when you’re standing in the middle of a party, “you’ll hear all these people talking, but you won’t hear anything in particular,” Kamionkowski said. .



This undated photo, submitted by researchers in June 2023, shows the Very Large Array radio telescope in New Mexico. This and several other telescopes around the world were used to observe the slow gravitational waves — weak waves produced by massive black holes — that are constantly stretching and compressing everything in the universe ever so slightly, as described in a report published Wednesday, June 28. 2023. Credit: NRAO/AUI/NSF via AP



Journalists and scientists attend a press conference to discuss the contribution of Chinese scientists at the National Astronomical Observatory of the Chinese Academy of Sciences (NAOC) using the Five Hundred Meter Aperture Spherical Telescope (FAST) in southern China to the International Cooperation on Gravitational Waves. ) in Beijing, Tuesday, June 27, 2023. On Wednesday, June 28, 2023, researchers reported signals from so-called low-frequency gravitational waves — changes in the structure of the universe caused by massive objects moving and colliding within it. space. It took scientists around the world decades of work to track down evidence of these ultra-slow fluctuations. Credit: AP Photo/Mark Schiefelbein








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

Researchers hope that continuing to study these types of gravitational waves can help us learn more about the largest objects in our universe. This could open new doors to “cosmic archaeology,” which can trace the history of black holes and galaxy mergers all around, Mark said.

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

More information:
Gabriella Agazie et al, The NANOGrav 15-year data set: Evidence for a gravitational wave background, Astrophysical Journal Letters (2023). DOI: 10.3847/2041-8213/acdac6

Magazine Details:
Astrophysical Journal Letters

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