![]() The timing is so precise that when Jocelyn Bell measured the first pulsar radio waves in 1967, astronomers thought they might be signals from an alien civilization.Īs a gravitational wave passes between us and a pulsar, it throws off the radio wave timing. The pulses arrive on Earth like a perfectly timed metronome. As the pulsars rapidly spin (sometimes hundreds of times a second), those beams sweep across the sky, appearing from our vantage point on Earth as rhythmic pulses of radio waves. Pulsars act like stellar lighthouses, shooting beams of radio waves from their magnetic poles. ![]() They closely observed pulsars, the ultra-dense remnants of massive stars that went supernova. No experiment on Earth could ever detect such colossal waves, so the NANOGrav team instead looked to the stars. Since gravitational waves travel at the speed of light, a single wavelength could be tens of light-years long. A single rise and fall of one of the waves could take years or even decades to pass by. Unlike the high-frequency waves detected by earthbound instruments such as LIGO and Virgo, the gravitational wave background is made up of ultra-low-frequency waves. The gravitational waves they hunted are different from anything previously measured. Getting to this point was a years-long challenge for the NANOGrav team. ![]() But there's also the possibility that something else is generating powerful gravitational waves, Mingarelli says, such as mechanisms predicted by string theory or alternative explanations of the universe's birth. "It's really at the upper end of what our models can create from just supermassive black holes." The deafening volume may result from experimental limitations or heavier and more abundant supermassive black holes. "The gravitational wave background is about twice as loud as what I expected," says Mingarelli, now an assistant professor at Yale University. The existence and composition of the gravitational wave background - long theorized but never before heard - presents a treasure trove of new insights into long-standing questions, from the fate of supermassive black hole pairs to the frequency of galaxy mergers.įor now, NANOGrav can only measure the overall gravitational wave background rather than radiation from the individual "singers." But even that brought surprises. We've opened a new window of observation on the universe." "This is the first-ever evidence for the gravitational wave background. "It's like a choir, with all these supermassive black hole pairs chiming in at different frequencies," says NANOGrav scientist Chiara Mingarelli, who worked on the new findings while an associate research scientist at the Flatiron Institute's Center for Computational Astrophysics (CCA) in New York City. Most of the gigantean gravitational waves are probably produced by pairs of supermassive black holes spiraling toward cataclysmic collisions throughout the cosmos, the NANOGrav scientists report in a series of new papers appearing today in The Astrophysical Journal Letters. The newly detected gravitational waves - ripples in the fabric of space-time - are by far the most powerful ever measured: They carry roughly a million times as much energy as the one-off bursts of gravitational waves from black hole and neutron star mergers detected by experiments such as LIGO and Virgo. The groundbreaking discovery was made by scientists with the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) who closely observed stars called pulsars that act as celestial metronomes. ![]() Following 15 years of data collection in a galaxy-sized experiment, scientists have "heard" the perpetual chorus of gravitational waves rippling through our universe for the first time - and it's louder than expected.
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