In a discovery that began generating excitement on social media before it was even announced, scientists have detected rippling gravitational waves more powerful than any identified before.
The news is revealed in a study published on June 28 in the journal Research in Astronomy and Astrophysics.
The research brought together scientists from more than 50 institutions in the U.S. and abroad, including the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), the National Science Foundation and the Flatiron Institute research division of the Simons Foundation.
These newly detected waves carry around a million times more energy than one-off gravitational waves previously found using Earth-based detectors, which emanate from intense gravitational events such as black hole and neutron star mergers.
The new discoveries are enormous background-level waves at extremely low frequencies, with a single peak and trough of one of the waves measuring tens of light-years.
“These are by far the most powerful gravitational waves known to exist,” Maura McLaughlin, co-director of the NANOgrav Physics Frontiers Center and an astrophysicist at West Virginia University, said in a Simons Foundation statement.
“Detecting such gargantuan gravitational waves requires a similarly massive detector, and patience.”
The waves are thought to have originated in the collisions of supermassive black holes, billions of years ago.
“The gravitational wave background is about twice as loud as what I expected. It’s really at the upper end of what our models can create from just supermassive black holes,” Chiara Mingarelli, an assistant professor at Yale and NANOGrav scientist, said in the Simons statement.
“It’s like a choir, with all these supermassive black hole pairs chiming in at different frequencies. This is the first-ever evidence for the gravitational wave background. We’ve opened a new window of observation on the universe.”
Mingarelli suggests that these waves may also have emerged due to other enormous bodies interacting, such as mechanisms predicted by string theory or even theories about the universe’s birth.
“What’s next is everything,” she said. “This is just the beginning.”
The waves were detected by using pulsars, which are rapidly spinning, immensely dense star remnants that shoot powerful beams of radio waves from their poles at regular intervals. Pulsars can act as stellar metronomes thanks to their regularity, making them an important asset in detecting gravitational waves, as the waves can distort the signals from the pulsars by stretching the fabric of space itself.
NANOGrav scientists observed an array of nearly 70 pulsars over 15 years, using data from collaborators from around the world, and found that they were distorted at points, leading to the discovery of background gravitational waves.
“The large number of pulsars used in the NANOGrav analysis has enabled us to see what we think are the first signs of the correlation pattern predicted by general relativity,” Xavier Siemens, co-director of the NANOGrav Physics Frontiers Center, said in a statement.
These huge waves have not been detected until now because they are much too large to be picked up by Earth-based detectors such as LIGO (the Laser Interferometer Gravitational-Wave Observatory) in the U.S. or Virgo in Italy.
Sethuraman Panchanathan, director of the National Science Foundation, said in the NANOGrav statement: “The NSF NANOGrav team created, in essence, a galaxy-wide detector revealing the gravitational waves that permeate our universe.
“The collaboration involving research institutions across the U.S. shows that world-class scientific innovation can, should and does reach every part of our nation.”
The researchers now want to use this discovery to study the objects thought to create the waves: supermassive black holes.
Initially, it wasn’t known exactly what happens when two supermassive black holes orbit each other, due to the pair stealing energy from each other to the point that the theories of thermodynamics break down.
Now it appears that the gravitational waves may be a way for the black holes to shed energy elsewhere, allowing them to finally collide.
“Once the two black holes get close enough to be seen by pulsar timing arrays, nothing can stop them from merging within just a few million years,” Luke Kelley, chair of NANOGrav’s astrophysics group and an astrophysicist at the University of California, Berkeley, said in the Simons statement.
Other possibilities for the source of the waves include alternative theories about the beginnings of the universe. One theory, known as the Big Bounce, suggests that the universe collapsed in on itself before expanding outwards again, which would have resulted in huge gravitational waves—like these—rippling through space-time even now.
In the years to come, the international teams will continue to work together to study the waves and their potential sources.
“Our combined data will be much more powerful,” said Stephen Taylor of Vanderbilt University in Nashville, Tennessee, who is chair of the NANOGrav collaboration. “We’re excited to discover what secrets they will reveal about our universe.”
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