A neutron star pileup may have emitted two different kinds of cosmic signals: ripples in spacetime known as gravitational waves and a brief blip of energy called a fast radio burst.

One of the three detectors that make up the gravitational wave observatory LIGO picked up a signal from a cosmic collision on April 25, 2019. About 2.5 hours later, a fast radio burst detector picked up a signal from the same region of sky, researchers report March 27 in Nature Astronomy.

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If strengthened by further observations, the finding could bolster the theory that mysterious fast radio bursts have multiple origins — and neutron star mergers are one of them.

“We’re 99.5 percent sure” the two signals came from the same event, says astrophysicist Alexandra Moroianu, who spotted the merger and its aftermath while at the University of Western Australia in Perth. “We want to be 99.999 percent sure.”

Unfortunately, LIGO’s two other detectors didn’t catch the signal, so it’s impossible to precisely triangulate its location. “Even though it’s not a concrete, bang-on observation for something that’s been theorized for a decade, it’s the first evidence we’ve got,” Moroianu says. “If this is true … it’s going to be a big boom in fast radio burst science.”

Mysterious radio bursts

Astronomers have spotted more than 600 fast radio bursts, or FRBs, since 2007. Despite their frequency, the causes remain a mystery. One leading candidate is a highly magnetized neutron star called a magnetar, which could be left behind after a massive star explodes (SN: 6/4/20). But some FRBs appear to repeat, while others are apparent one-off events, suggesting that there’s more than one way to produce them (SN: 2/7/20).

Theorists have wondered if a collision between two neutron stars could spark a singular FRB, before the wreckage from the collision produces a black hole. Such a smashup should emit gravitational waves, too (SN: 10/16/17).

Moroianu and colleagues searched archived data from LIGO and the Canadian Hydrogen Intensity Mapping Experiment, or CHIME, a fast radio burst detector in British Columbia, to see if any of their signals lined up. The team found one candidate pairing: GW190425 and FRB20190425A.

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Even though the gravitational wave was picked up only by the LIGO detector in Livingston, La., the team spotted other suggestive signs that the signals were related. The FRB and the gravitational waves came from the same distance, about 370 million light-years from Earth. The gravitational waves were from the only neutron star merger LIGO spotted in that observing run, and the FRB was particularly bright. There may even have been a burst of gamma rays at the same time, according to satellite data — another aftereffect of a neutron star merger.

“Everything points at this being a very interesting combination of signals,” Moroianu says. She says it’s like watching a crime drama on TV: “You have so much evidence that anyone watching the TV show would be like, ‘Oh, I think he did it.’ But it’s not enough to convince the court.”

Neutron star secrets

Despite the uncertainty, the finding has exciting implications, says astrophysicist Alessandra Corsi of Texas Tech University in Lubbock. One is the possibility that two neutron stars could merge into a single, extra-massive neutron star without immediately collapsing into a black hole. “There’s this fuzzy dividing line between what’s a neutron star and what’s a black hole,” says Corsi, who was not involved in the new work.

In 2013, astrophysicist Bing Zhang of the University of Nevada, Las Vegas suggested that a neutron star smashup could create an extra-massive neutron star that wobbles on the edge of stability for a few hours before collapsing into a black hole. In that case, the resulting FRB would be delayed — just like in the 2019 case.

The most massive neutron star yet observed is about 2.35 times the mass of the sun, but theorists think they could grow to be around three times the mass of the sun without collapsing (SN: 7/22/22). The neutron star that could have resulted from the collision in 2019 would have been 3.4 solar masses, Moroianu and colleagues calculate.

“Something like this, especially if it’s confirmed with more observations, it would definitely tell us something about how neutron matter behaves,” Corsi says. “The nice thing about this is we have hopes of testing this in the future.”

The next LIGO run is expected to start in May. Corsi is optimistic that more coincidences between gravitational waves and FRBs will show up, now that researchers know to look for them. “There should be a bright future ahead of us,” she says. More

A chance alignment may have revealed a star from the universe’s first billion years.

If confirmed, this star would be the most distant one ever seen, obliterating the previous record (SN: 7/11/17). Light from the star traveled for about 12.9 billion years on its journey toward Earth, about 4 billion years longer than the former record holder, researchers report in the March 30 Nature. Studying the object could help researchers learn more about the universe’s composition during that early, mysterious time.

“These are the sorts of things that you only hope you could discover,” says astronomer Katherine Whitaker of the University of Massachusetts Amherst, who was not part of the new study.

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The researchers found the object while analyzing Hubble Space Telescope images of dozens of clusters of galaxies nearer to Earth. These clusters are so massive that they bend and focus the light from more distant background objects, what’s known as gravitational lensing (SN: 10/6/15).

In images of one cluster, astronomer Brian Welch of Johns Hopkins University and colleagues noticed a long, thin, red arc. The team realized that the arc was a background galaxy whose light the cluster had warped and amplified.

Atop that red arc is a bright spot that is too small to be a small galaxy or a star cluster, the researchers say. “We stumbled into finding that this was a lensed star,” Welch says.

The researchers estimate that the star’s light originates from only 900 million years after the Big Bang, which took place about 13.8 billion years ago.

Welch and his colleagues think that the object, which they poetically nicknamed “Earendel” from the old English word meaning “morning star” or “rising light,” is a behemoth with at least 50 times the mass of the sun. But the researchers can’t pin down that value, or learn more about the star or even confirm that it is a star, without more detailed observations.

The researchers plan to use the recently launched James Webb Space Telescope to examine Earendel (SN: 10/6/21). The telescope, also known as JWST, will begin studying the distant universe this summer.

JWST may uncover objects from even earlier times in the universe’s history than what Hubble can see because the new telescope will be sensitive to light from more distant objects. Welch hopes that the telescope will find many more of these gravitationally lensed stars. “I’m hoping that this record won’t last very long.” More

Something’s fishy in the southern constellation Phoenix.

Strange radio emissions from a distant galaxy cluster take the shape of a gigantic jellyfish, complete with head and tentacles. Moreover, the cosmic jellyfish emits only the lowest radio frequencies and can’t be detected at higher frequencies. The unusual shape and radio spectrum tell a tale of intergalactic gas washing over galaxies and gently revving up electrons spewed out by gargantuan black holes long ago, researchers report in the March 10 Astrophysical Journal.

Spanning 1.2 million light-years, the strange entity lies in Abell 2877, a cluster of galaxies 340 million light-years from Earth. Researchers have dubbed the object the USS Jellyfish, because of its ultra-steep spectrum, or USS, from low to high radio frequencies.

“This is a source which is invisible to most of the radio telescopes that we have been using for the last 40 years,” says Melanie Johnston-Hollitt, an astrophysicist at Curtin University in Perth, Australia. “It holds the record for dropping off the fastest” with increasing radio frequency.

Johnston-Hollitt’s colleague Torrance Hodgson, a graduate student at Curtin, discovered the USS Jellyfish while analyzing data from the Murchison Widefield Array, a complex of radio telescopes in Australia that detect low-frequency radio waves. These radio waves are more than a meter long and correspond to photons, particles of light, with the lowest energies. Remarkably, the USS Jellyfish is about 30 times brighter at 87.5 megahertz — a frequency similar to that of an FM radio station — than at 185.5 MHz.

The Murchison Widefield Array consists of 4,096 radio antennas grouped into 256 “tiles” (one pictured) spanning several kilometers in a remote region of Western Australia.Pete Wheeler, ICRAR

“That is quite spectacular,” says Reinout van Weeren, an astronomer at Leiden University in the Netherlands who was not involved with the work. “It is quite a neat result, because this is really extreme.”

The USS Jellyfish bears no relation to previously discovered jellyfish galaxies. “This is absolutely enormous compared to those other things,” Johnston-Hollitt says. Indeed, jellyfish galaxies are a very different kettle of celestial fish. Although they also inhabit galaxy clusters, they are individual galaxies passing through hot gas in a cluster. The hot gas tears the galaxy’s own gas out of it, creating a wake of tentacles. The much larger USS Jellyfish, on the other hand, appears to have formed when intergalactic gas and electrons interacted.

Hodgson and his colleagues note that two galaxies in the Abell 2877 cluster coincide with the brightest patches of radio waves in the USS Jellyfish’s head. These galaxies, the researchers say, probably have supermassive black holes at their centers. The team ran computer simulations and found that the black holes were probably accreting material some 2 billion years ago. As they did so, disks of hot gas formed around each of them, spewing huge jets of material into the surrounding galaxy cluster.

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This ejected material had electrons that whirled around magnetic fields at nearly the speed of light, so the electrons emitted radio waves. Over time, though, the electrons lost energy, and the most energetic electrons, which had been emitting the highest radio frequencies, faded the most. Then a wave of gas sloshed through the entire cluster, reaccelerating the electrons around the two galaxies.

“It’s a very gentle process,” Johnston-Hollitt says. “The electrons don’t get that much energy, which means they don’t light up at high frequencies.” Instead, the gentle gas wave caused electrons to emit radio waves with the lowest energies and frequencies, giving the USS Jellyfish the extreme spectrum it has today. More

Caught in a fatal inward spiral, a neutron star met its end when a black hole swallowed it whole. Gravitational ripples from that collision spread outward through the cosmos, eventually reaching Earth. The detection of those waves marks the first reported sighting of a black hole engulfing the dense remnant of dead star. And in a surprise twist, scientists spotted a second such merger just days after the first.

Until now, all identified sources of gravitational waves were twos of a kind: either two black holes or two neutron stars, spiraling around one another before colliding and coalescing (SN: 1/21/21). The violent cosmic collisions create waves that stretch and squeeze the fabric of spacetime, undulations that can be sussed out by sensitive detectors.

The mismatched pairing of a black hole and neutron star was the final type of merger that scientists expected to find with current gravitational wave observatories. By pure coincidence, researchers spotted two of these events within 10 days of one another, the LIGO, Virgo and KAGRA collaborations report in the July 1 Astrophysical Journal Letters.

Not only have unions between black holes and neutron stars not been seen before via gravitational waves, the smashups have also never been spotted at all by any other means.

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“This is an absolute first look,” says theoretical physicist Susan Scott of the Australian National University in Canberra, a member of the LIGO collaboration.

The result adds another tick mark to the tally of new discoveries made with gravitational waves. “That’s worth celebration,” says astrophysicist Cole Miller of the University of Maryland in College Park, who was not involved with the research. Since the first gravitational waves were detected in 2015, the observatories keep revealing new secrets. “It’s fantastic new things; it’s not just the same old, same old,” he says.

Signs of the black hole-neutron star collisions registered in the LIGO and Virgo gravitational wave observatories in 2020, on January 5 and January 15. The first merger consisted of a black hole about 8.9 times the mass of the sun and a neutron star about 1.9 times the sun’s mass. The second merger had a 5.7 solar mass black hole and a 1.5 solar mass neutron star. Both collisions occurred more than 900 million light-years from Earth, the scientists estimate.

To form detectable gravitational waves, the objects that coalesce must be extremely dense, with identities that can be pinned down by their masses. Anything with a mass above five solar masses could only be a black hole, scientists think. Anything less than about three solar masses must be a neutron star.

One earlier gravitational wave detection involved a black hole merging with an object that couldn’t be identified, as its mass seemed to fall in between the cutoffs that separate black holes and neutron stars (SN: 6/23/20). Another previous merger may have resulted from a black hole melding with a neutron star, but the signal from that event wasn’t strong enough for scientists to be certain that the detection was the real deal. The two new detections clinch the case for black hole and neutron star meetups.

One of the new events is more convincing than the other. The Jan. 5 merger was seen in just one of LIGO’s two gravitational wave detectors, and the signal has a relatively high probability of being a false alarm, Miller says. “If this were the only event, then you would not be as confident.” The Jan. 15 event, however, “seems pretty solid,” he says.

Epic rendezvous between neutron stars and black holes happen regularly throughout the cosmos, the detections suggest. Based on the pace of detections, the researchers estimate that these events take place about once a month within 1 billion light-years of Earth.

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In a newly reported class of cosmic smashup, a neutron star (apparent in orange in this computer simulation, after the video zooms in) and black hole (dark gray) spiral inward, producing gravitational waves (blue) in a dance that ends when the black hole swallows the neutron star.

Scientists don’t yet know how neutron stars and black holes come to meet up. They might form together, as two stars that orbit one another until both run out of fuel and die, with one collapsing into a black hole and the other forming a neutron star. Or the two objects might have formed separately and met up in a crowded region packed with many neutron stars and black holes.

As a black hole and neutron star spiral inward and merge, scientists expect that the black hole could rip the neutron star to shreds, producing a light show that could be observed with telescopes. But astronomers found no fireworks in the aftermath of the two newly reported encounters, nor any evidence that the black holes deformed the neutron stars.

That could be because in both cases the black hole was significantly larger than the neutron star, suggesting that the black hole gulped down the neutron star whole in a meal worthy of Pac-Man, Scott says.

If scientists could spot a black hole shredding a neutron star in the future, that could help researchers pin down the properties of the ultradense, neutron-rich material that makes up the dead stars (SN: 4/20/21).

In past detections of gravitational waves, the Advanced Laser Interferometer Gravitational-Wave Observatory, or LIGO, based in the United States, has teamed up with Virgo, in Italy. The new observations are the first to include members of a third observatory, KAGRA, in Japan (SN: 1/18/19). But the KAGRA detector itself didn’t contribute to the results, as scientists were still preparing it to detect gravitational waves at the time. LIGO, Virgo and KAGRA are all currently offline while scientists tinker with the detectors, and will resume their communal search for cosmic collisions in 2022. More

The oldest disk-shaped galaxy ever spotted formed just 1.5 billion years after the Big Bang, a new study finds. That’s much earlier than astronomers thought that this type of galaxy could form. Previous observations show that disk-shaped galaxies — including sprawling, spiral systems like the Milky Way — didn’t show up in large numbers until […] More