![]() He says the possibilities range from cosmic strings to dark matter to primordial black holes that formed soon after the Big Bang. "The theorists have really had a lot of fun coming up with models that can produce very similar types of gravitational wave signals," says Luke Zoltan Kelley, a theoretical astrophysicist at Northwestern University and NANOGrav. What they see is consistent with predictions about supermassive black holes, but it could be something even more unusual. The researchers don't yet know what's creating these waves. Rather than seeing one wave come rolling in, like someone standing on a beach, he says, it's more like the experience of swimming out in a choppy ocean. "It's really hard to attribute that the waves are coming from one direction or another," says Hazboun. What they found is a pattern of deviations from the expected pulsar beam arrival timings that suggests gravitational waves are jiggling space-time as though it's a vast serving of Jell-O. ![]() In their latest analysis, which is being published in a series of papers in The Astrophysical Journal Letters, the researchers looked at data from about 70 pulsars. "And if that pulse is a little bit late or a little bit early, then we may be able to attribute that to a gravitational wave passing through," says Hazboun, who explains that a gravitational wave will stretch or compress space-time, changing the distance that a pulse has to travel to get to Earth. They can then look for tiny deviations from that expected arrival time. The intervals are so regular that scientists can predict exactly when a pulse should arrive at Earth. "These pulses arrive at stunningly regular intervals." "Each time their beam crosses our line of sight, we see a pulse signal," says NANOGrav collaboration member Thankful Cromartie of Cornell University. That landmark discovery showed that gravitational waves truly existed, fulfilling a prediction made by Albert Einstein in 1916 and giving researchers a new way to study exotic phenomena like black holes and neutron stars. The first were seen in 2015, when a research consortium registered the waves created by the merger of two black holes that were each about 30 times as massive as the sun. Until now, scientists have only been able to detect gravitational waves created by much smaller black holes. Other research groups using telescopes in Europe, Australia, India, and China also say they're starting to see hints of these waves. ![]() "We're very happy to announce that our hard work has paid off." "We've been on a mission for the last fifteen years to find a low-pitched hum of gravitational waves resounding throughout the universe," says Stephen Taylor, a Vanderbilt University astrophysicist who serves as the chair of a team of researchers known as the North American Nanohertz Observatory for Gravitational Waves ( NANOGrav). Machines That Hunt For Ripples In Space-Time Just Got An Upgrade
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