Scientists may have just found the longest gravitational waves yet.



Gravitational waves are ripples in the fabric of spacetime. Kicked up by massive objects, they roll through the universe like water waves on the surface of the ocean. The newfound gravitational waves are light-years long. That means it would take years for light to travel the distance of a single ripple.



Explainer: What are gravitational waves?



Whats more, these waves wash through the universe nonstop. They constantly jostle Earth and the rest of our galaxy.





Pairs of huge supermassive black holes are thought to trigger these waves. Those black-hole behemoths sit at the centers of galaxies. Scientists think that when two galaxies collide, their black holes pair up and orbit each other. This action could churn up those gravitational waves in spacetime.



Indeed, across the universe, galaxies often mingle and merge. As they do, scientists had suspected their supermassive black holes would orbit each other. In the process, these black holes would give off gravitational waves. In fact, they should pump out waves nonstop for millions of years. Many supermassive-black-hole pairs in the many merging galaxies across the cosmos would send out their spacetime ripples at once. This, scientists thought, should create a constant mishmash of very long gravitational waves.



Explainer: What are black holes?



On June 28, researchers shared the first clear evidence of such a background of gravitational waves. Those data came from several teams around the world.



Scientists must confirm that the newly spotted waves are real and that they do come from pairs of huge black holes. But if so, its miraculous, says Meg Urry. Shes an astrophysicist at Yale University. Thats in New Haven, Conn.



Confirming the new findings would offer the first proof that the biggest black holes in the cosmos can spiral into each other and merge. Its extremely interesting, Urry says. The reason? We have essentially no handle on what the most massive black holes are doing.



Catching a new kind of wave



Since 2015, scientists have spotted lots of gravitational waves. Some have come from smashups between neutron stars. Others have come from colliding black holes. But the black holes in those collisions were small, by cosmic standards. Most were less than 100 times the mass of our sun. Their smashups created blips of gravitational waves that detectors on Earth felt for mere fractions of a second.



Those supermassive black holes thought to cause the newfound gravitational waves are entirely different beasts. Each can have the mass of millions or billions of suns.



The Earth is just randomly bumping around on this sea of gravitational waves, says Maura McLaughlin. Shes an astrophysicist at West Virginia University in Morgantown.





Compared to the gravitational waves seen before, this is a very different sort of thing, says Daniel Holz. This astrophysicist works at the University of Chicago, in Illinois. He and others have used the LIGO detector to spot gravitational-wave blips from small black-hole smashups.



To find waves from supermassive black holes required a whole new technique.





Peering at pulsars



For this new research, scientists looked to objects called pulsars. Theyre spinning remnants of exploded stars. Like celestial lighthouses, pulsars emit beams of radio waves as they spin. Their beams sweep past Earth at regular intervals. Those flashing beams of radio waves are picked up, like the precise ticks of a clock, by telescopes on Earth.



Gravitational waves can stretch and squeeze the space between a pulsar and Earth. In that way, such ripples in spacetime could cause a pulsars ticks to reach Earth early or late. Scientists have now used this effect to search for the gravitational waves from supermassive black holes as they roll through space.



A project called NANOGrav has watched dozens of pulsars for 15 years. (NANOGrav is short for North American Nanohertz Observatory for Gravitational Waves.) The NANOGrav team now thinks it finally has evidence of gravitational waves from pairs of supermassive black holes. The team just shared its findings in Astrophysical Journal Letters.



Scientists searched for gravitational waves by watching dozens of spinning stars called pulsars. Here, each pulsar is shown as a blue dot against a gray illustration of our Milky Way galaxy. The yellow star (near center) shows where Earth sits in the Milky Way.NANOGrav


Its really invigorating stuff, says Michael Keith. Hes an astrophysicist at the University of Manchester in England. Hes also a member of the European Pulsar Timing Array, or EPTA.



The EPTA team spent an even longer time staring at pulsars about 25 years. We were starting to think maybe the signal is just so weak, well never ever find it, Keith says. But like NANOGrav, EPTA has now seen evidence for gravitational waves altering pulsar signals.



EPTAs results have been accepted in the journal Astronomy and Astrophysics. The European group teamed up with researchers from the Indian Pulsar Timing Array to do the work. Teams from Australia and China have now shared evidence for gravitational waves from pairs of supermassive black holes, too.



Astronomers used a variety of radio telescopes to view pulsars in their hunt for gravitational waves. One of those telescopes was the Effelsberg radio telescope (shown) in Germany.Tacken, MPIfR


Its not over yet



Some scientists had thought that supermassive black holes in merging galaxies would never draw close enough to merge. In that case, they wouldnt give off gravitational waves like the ones scientists think they have now observed.



Its actually been a sore spot for our field for many years, Chiara Mingarelli says. Mingarelli is an astrophysicist on the NANOGrav team. Shes based at Yale University.



But if the new gravitational-wave signal is real, it seems to be stronger than expected. That suggests that supermassive black holes spiraling into each other are common. This, in turn, hints that mergers between such black holes also are common.



But none of the teams sharing new data say they have for sure detected gravitational waves from huge black-hole pairs. They just say theyve found strong evidence for this. Thats because each of their observations comes with some uncertainty. In the future, the separate teams plan to join forces. Combining their data may help confirm the detection.



Still, even if the waves are real, its possible they dont come from pairs of monster black holes. Such huge black holes appear to be the simplest explanation. Still, researchers cant rule out a more exotic one. For example, the ripples might have arisen from the fast expansion of the universe just after the Big Bang.



Learning more about supermassive black holes is key to understanding the galaxies that host them. So whatever the source of the potential new gravitational waves, their future study is bound to have ripple effects.

Northern elephant seals are the true masters of the power nap.



These marine mammals swim at sea for months between brief breaks on shore. During those sea voyages, the seals snooze less than 20 minutes at a time. On average, they get a total of just two hours of shut-eye per day.



This extreme sleep schedule rivals African elephants for the least sleep seen among mammals.



Researchers shared the discovery in the April 21 Science.



Its important to map these extremes of [sleep behavior] across the animal kingdom, says Jessica Kendall-Bar. She studies marine mammals at the University of California, San Diego. Learning how much or how little sleep different animals get could help reveal why animals, including people, sleep at all.





Knowing how seals catch their zzzs also could guide efforts to protect places where they sleep.





Tracking seal sleep



Northern elephant seals (Mirounga angustirostris) spend most of the year in the Pacific Ocean. At sea, those animals hunt around the clock for fish, squid and other food.



The elephant seals, in turn, are hunted by sharks and killer whales. The seals are most vulnerable to such predators at the sea surface. So they come up for air only a couple minutes at a time between 10- to 30-minute dives.



People had known that these seals dive almost all the time when theyre out in the ocean. But it wasnt known if and how they sleep, notes Niels Rattenborg. He wasnt involved in the new study, but he has studied animal sleep. He works in Seewiesen, Germany, at the Max Planck Institute for Biological Intelligence.



Explainer: How to read brain activity



Kendall-Bars team wanted to find out if northern elephant seals really do sleep while diving. To do this, the researchers outfitted two northern elephant seals with special caps. Those caps recorded the animals brain waves, revealing when they were asleep. Motion sensors were also strapped onto the seals.



By looking at both brain-wave readings and motion data, the researchers could see how seals moved while asleep.



Kendall-Bars team took their two seals from Ao Nuevo State Park. Thats on the coast of California, north of Santa Cruz. The researchers then released the seals at another beach, one about 60 kilometers (37 miles) south of Ao Nuevo. To swim home, the seals had to cross the deep Monterey Canyon. The waters here are similar to those in the deep Pacific, where the seals swim during their months-long trips at sea.





Matching the seals brain-wave readings to their diving motions on this journey showed how northern elephant seals get their sleep on long voyages.



Deep-sea snoozes



The data revealed that when a northern elephant seal wants to sleep at sea, it first dives 60 to 100 meters (200 to 360 feet) below the surface. Then, it relaxes into a glide. As the seal nods off, it keeps holding itself upright for several minutes.



But then, the seal slips into a stage of rest known as REM sleep. During this sleep stage, the animals body becomes paralyzed. A slumbering seal now flips upside-down and drifts in a gentle spiral toward the seafloor.



A northern elephant seal can descend hundreds of meters (yards) deep during one of these naps. Thats far below the waters where sharks and killer whales normally prowl. When a seal wakes after a five- to 10-minute nap, it swims back to the surface. The whole routine takes about 20 minutes.



Explainer: Tagging through history



Now that Kendall-Bars team knew how seals moved during sleep, they could pick out naps in motion data from other seals who hadnt been outfitted with the special caps.



The researchers looked for naptime dive motions in tracking data on 334 other northern elephant seals. Those seals had been outfitted with tracking tags from 2004 to 2019. The seals movements revealed that while at sea these creatures conk out, on average, only around two hours per day.



But northern elephant seals arent short on sleep all the time. They snooze nearly 11 hours per day when they come on land to mate and molt. On the beach, they can catch up on sleep without worrying about getting eaten.



What the seals are doing [at the beach] might be something like what we do when we sleep in on the weekend, Rattenborg says.



Northern elephant seal naps are no joke. While on land, these animals can conk out for a solid 11 hours per day. But at sea, the seals catch only brief bits of sleep.Photo by Jessica Kendall-Bar, NMFS 23188



Extreme animal sleep



Northern elephant seals arent the only animals that sleep very little, at times, and then a whole lot. Rattenborgs group has found a similar sleep pattern in great frigate birds. They fly over the ocean. They can sleep while theyre flying, Rattenborg says. So on those trips, they sleep less than an hour a day for up to a week at a time, he says. Once back on land, they sleep over 12 hours a day.



Curiously, the sleep habits of northern elephant seals seem quite different from those of other marine mammals. When studied in the lab, many marine mammals sleep with just half their brain at a time. That half-awake state allows dolphins, fur seals and sea lions to constantly watch for predators. They literally sleep with one eye open.



Its pretty cool that elephant seals get by without one-sided sleep, Kendall-Bar says. Theyre shutting off both halves of their brain completely and leaving themselves vulnerable. Diving far below predators is what allows the seals to rest easy.



It seems the key to their enjoying such deep sleep is sleeping deep in the sea.