Space & Astronomy

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 rocky planet that circles a small star nearly 40 light-years from Earth is hot and has little or no atmosphere, a new study suggests. The finding raises questions about the possibility of atmospheres on the other orbs in the planetary system.

At the center of the system is the red dwarf star dubbed TRAPPIST-1; it hosts seven known planets with masses ranging from 0.3 to 1.4 times Earth’s, a few of which could hold liquid water (SN: 2/22/17; 3/19/18). The largest, TRAPPIST-1b, is the closest to its parent star and receives about four times the radiation Earth receives from the sun, says Thomas Greene, an astrobiologist at NASA’s Ames Research Center at Moffett Field, Calif.

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Like all other planets in the system, TRAPPIST-1b is tidally locked, meaning that one side of the planet always faces the star, and one side looks away. Calculations suggest that if the stellar energy falling on TRAPPIST-1b were distributed around the planet — by an atmosphere, for example — and then reradiated equally in all directions, the planet’s surface temperature would be around 120° Celsius.

But the dayside temperature of the planet is actually around 230° C, Greene and colleagues report online March 27 in Nature. That, in turn, suggests that there’s little or no atmosphere to carry heat from the perpetually sunlit side of the planet to the dark side, the team argues.

To take TRAPPIST-1b’s temperature, Greene and his colleagues used the James Webb Space Telescope to observe the planet in a narrow band of infrared wavelengths five times in 2022. Because the observations were made just before and after the planet dodged behind its parent star, astronomers could see the fully lit face of the planet, Greene says.

The team’s results are “the first ‘deep dive’ look at this planet,” says Knicole Colon, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Md, who was not involved with the study. “With every observation, we expect to learn something new,” she adds.

Astronomers have long suggested that planets around red dwarf stars might not be able to hold onto their atmospheres, largely because such stars’ frequent and high-energy flares would blast away any gaseous shroud they might have during their early years (SN: 12/20/22). Yet there are some scenarios in which such flares could heat up a planet’s surface and drive volcanism that, in turn, yields gases that could help form a new atmosphere.

“To be totally sure that this planet has no atmosphere, we need many more measurements,” says Michaël Gillon, an astrophysicist at the University of Liège in Belgium who was not part of the new study. It’s possible that when observed at a wider variety of wavelengths and from other angles, the planet could show signs of a gaseous shroud and thus possibly hints of volcanism.

Either way, says Laura Kriedberg, an astronomer at the Max Planck Institute for Astronomy in Heidelberg, Germany, who also did not participate in the study, the new result “definitely motivates detailed study of the cooler planets in the system, to see if the same is true of them.” More

17th century scientist Christiaan Huygens set his sights on faraway Saturn, but he may have been nearsighted.

Huygens is known, in part, for discovering Saturn’s largest moon, Titan, and deducing the shape of the planet’s rings. But by some accounts, the Dutch scientist’s telescopes produced fuzzier views than others of the time despite having well-crafted lenses.

That may be because Huygens needed glasses, astronomer Alexander Pietrow proposes March 1 in Notes and Records: the Royal Society Journal of the History of Science.

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To make his telescopes, Huygens combined two lenses, an objective and an eyepiece, positioned at either end of the telescope. Huygens experimented with different lenses to find combinations that, to his eye, created a sharp image, eventually creating a table to keep track of which combinations to use to obtain a given magnification. But when compared with modern-day knowledge of optics, Huygens’ calculations were a bit off, says Pietrow, of the Leibniz Institute for Astrophysics Potsdam in Germany.

One possible explanation: Huygens selected lenses based on his flawed vision. Historical records indicate that Huygens’ father was nearsighted, so it wouldn’t be surprising if Christiaan Huygens also suffered from the often-hereditary affliction.

Assuming that’s the reason for the mismatch, Pietrow calculates that Huygens had 20/70 vision: What someone with normal vision could read from 70 feet away, Huygens could read only from 20 feet. If so, that could be why Huygens’ telescopes never quite reached their potential. More