The sweeping beams of cosmic lighthouses called pulsars are much more energetic than previously thought, calling into question the bulbs that power them.
A new analysis, from the High Energy Stereoscopic System array in Namibia, reveals a pulsar that radiates at 20 trillion electron volts — making it the most energetic pulsar ever seen. The finding, described October 5 in Nature Astronomy, is challenging scientists’ understanding of how pulsars can emit such extreme radiation.
The observation is “spectacular,” says Hayk Hakobyan, an astrophysicist at Columbia University who was not part of the study. “This is basically a stress test for our theories.”
Pulsars are the dense remnants of exploded stars, emitting beams of light as they twirl up to hundreds of times a second. Pulsars were first discovered in the late 1960s, from a throb of radio waves so consistent that some suggested it was an alien broadcast (SN: 3/8/18).
As a pulsar rotates, its massive magnetic field rips charged particles from the surface, ejecting them along magnetic field lines and spitting radiation out the pulsar’s poles. Over the decades, scientists have found pulsars that beam radiation at higher energies, topping off at about a trillion electron volts, as observed in the Crab pulsar in 2016.
In the new study, scientists analyzed 80 hours of data from the Namibian array, which looks for a wake of light given off when high-energy light emitted elsewhere in the universe crashes into molecules in Earth’s atmosphere. The researchers identified 78 super-energetic particles of light that they traced to a pulsar about 1,000 light-years from Earth, in the constellation Vela. That light, the team determined, had at least 20 times higher energy than the Crab pulsar observation.
The team first spotted hints of the mighty radiation a few years ago and struggled to interpret the data. “This discovery was so unexpected … that it somehow was difficult to understand,” says Arache Djannati-Ataï, an astrophysicist at CNRS in Paris, who led the analysis.
To reach such high energies, the light is probably boosted by collisions with other speedy, energetic particles such as electrons. But how it becomes so energetic is still up for debate.
The new finding lends support to the growing idea that, thousands of kilometers from a pulsar’s surface, its magnetic field lines can collide and snap, launching particles to extreme speeds in a process called magnetic reconnection. But the observed radiation is pushing the limit of how much energy the reconnection process can release, and scientists will have to scramble for new explanations if higher-energy pulsar radiation keeps turning up.
The possibility of extreme pulsar radiation had been looming over theorists, Hakobyan says. “But now, it’s definite. So now, you have to go do something about it.” More
Newly christened “Dimorphos” is a tiny space rock with a big target on its back. The International Astronomical Union gave the rock an official name on June 23 for a unique reason: It has been marked for the first-ever asteroid deflection mission. A NASA spacecraft will ram into Dimorphos — on purpose — to alter […] More
Flashes of CreationPaul HalpernBasic Books, $30
The Big Bang wasn’t always a sure bet. For several decades in the 20th century, researchers wrestled with interpreting cosmic origins, or if there even was a beginning at all. At the forefront of that debate stood physicists George Gamow and Fred Hoyle: One advocated for an expanding universe that sprouted from a hot, dense state; the other for a cosmos that is eternal and unchanging. Both pioneered contemporary cosmology, laid the groundwork for our understanding of where atoms come from and brought science to the masses.
In Flashes of Creation, physicist Paul Halpern recounts Gamow’s and Hoyle’s interwoven stories. The book bills itself as a “joint biography,” but that is a disservice. While Gamow and Hoyle are the central characters, the book is a meticulously researched history of the Big Bang as an idea: from theoretical predictions in the 1920s, to the discovery of its microwave afterglow in 1964, and beyond to the realization in the late 1990s that the expansion of the universe is accelerating.
Although the development of cosmology was the work of far more than just two scientists, Halpern would be hard-pressed to pick two better mascots. George Gamow was an aficionado of puns and pranks and had a keen sense of how to explain science with charm and whimsy (SN: 8/28/18). The fiercely stubborn Fred Hoyle had a darker, more cynical wit, with an artistic side that showed through in science fiction novels and even the libretto of an opera. Both wrote popular science books — Gamow’s Mr Tompkins series, which explores modern physics through the titular character’s dreams, are a milestone of the genre — and took to the airwaves to broadcast the latest scientific thinking into people’s homes.
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“Gamow and Hoyle were adventurous loners who cared far more about cosmic mysteries than social conventions,” Halpern writes. “Each, in his own way, was a polymath, a rebel, and a master of science communication.”
While the Big Bang is now entrenched in the modern zeitgeist, it wasn’t always so. The idea can be traced to Georges Lemaître, a physicist and priest who proposed in 1927 that the universe is expanding. A few years later, he suggested that perhaps the cosmos began with all of its matter in a single point — the “primeval atom,” he called it. In the 1940s, Gamow latched on to the idea as way to explain how all the atomic elements came to be, forged in the “fireball” that would have filled the cosmos in its earliest moments. Hoyle balked at the notion of a moment of creation, convinced that the universe has always existed — and always will exist — in pretty much the same state we find it today. He even coined the term “Big Bang” as a put-down during a 1949 BBC radio broadcast. The elements, Hoyle argued, were forged in stars.
As far as the elements go, both were right. “One wrote the beginning of the story of element creation,” Halpern writes, “and the other wrote the ending.” We now know that hydrogen and helium nuclei emerged in overwhelming abundance during the first few minutes following the Big Bang. Stars took care of the rest.
Halpern treats Gamow and Hoyle with reverence and compassion. Re-created scenes provide insight into how both approached science and life. We learn how Gamow, ever the scientist, roped in physicist Niels Bohr to test ideas about why movie heroes always drew their gun faster than villains — a test that involved staging a mock attack with toy pistols. We sit in with Hoyle and colleagues while they discuss a horror film, Dead of Night, whose circular timeline inspired their ideas about an eternal universe.
In the mid-20th century, two astronomers emerged as spokesmen for dueling ideas about the origin of the cosmos. George Gamow (left) was a passionate defender of the Big Bang theory, arguing that the universe evolved from a hot, dense state. Fred Hoyle (right) upheld the rival “steady state model,” insisting that the universe is eternal and unchanging.From left: AIP Emilio Segrè Visual Archives, George Gamow Collection; AIP Emilio Segrè Visual Archives, Clayton Collection
And Halpern doesn’t shy away from darker moments, inviting readers to know these scientists as flawed human beings. Gamow’s devil-may-care attitude wore on his colleagues, and his excessive drinking took its toll. Hoyle, in his waning decades, embraced outlandish ideas, suggesting that epidemics come from space and that a dinosaur fossil had been tampered with to show an evolutionary link to birds. And he went to his grave in 2001 still railing against the Big Bang.
Capturing the history of the Big Bang theory is no easy task, but Halpern pulls it off. The biggest mark against the book, in fact, may be its scope. To pull in all the other characters and side plots that drove 20th century cosmology, Gamow and Hoyle sometimes get forgotten about for long stretches. A bit more editing could have sharpened the book’s focus.
But to anyone interested in how the idea of the Big Bang grew — or how any scientific paradigm changes — Flashes of Creation is a treat and a worthy tribute to two scientific mavericks.
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A long-ago reshuffling of the giant planets in our solar system may have been instrumental in giving Earth its moon.
For decades, planetary scientists have hypothesized that Jupiter, Saturn, Uranus and Neptune were born much closer to the sun and that gravitational interactions among those planets jolted them into their contemporary trajectories (SN: 5/10/22). But the timing of that “giant planet orbital instability” has been tricky to nail down.
Now, an analysis of meteorite data suggests that the instability took place between 60 million and 100 million years after the solar system started forming, planetary scientist Alessandro Morbidelli reported October 5 in San Antonio at a meeting of the American Astronomical Society’s Division for Planetary Sciences. That timing also roughly coincides with when Earth’s moon is thought to have formed in the wake of a Mars-sized planet running into our own.
The instability of the giant planets “is related to a complete reshaping of the solar system, the formation of the cometary reservoirs, the sculpting of the asteroid belt,” says Morbidelli, of the Observatoire de la Côte d’Azur in Nice, France. “Understanding when it occurred means fixing a milestone in the history of the solar system.”
The giant planet migration, first proposed by Morbidelli and colleagues in 2005, is a widely accepted hypothesis for explaining much about the solar system. In particular, the giant planets travel along slightly elongated orbits that are askew to one another. But observations of other planetary systems and computer simulations of planet formation suggest that giant planets, in general, form on closer-in orbits that are circular and coplanar. Using simulations, Morbidelli and others showed that if the giant planets in our solar system formed like that, they wouldn’t stay that way. Gravitational interactions would eventually knock the planets into the orbits they have today.
At first, the team thought this instability occurred about 600 million years after the birth of the solar system. That timing meant the migration of the giant planets could also explain an apparent asteroid bombardment of the terrestrial planets — Mercury, Venus, Earth and Mars — as evidenced by craters on the moon and lunar rocks brought back by Apollo astronauts. More recent work, however, has cast doubt on the reality of this “lunar cataclysm.”
Now, Morbidelli suspects the orbital instability came a lot earlier. His reasoning starts with a rare type of meteorite called EL enstatite chondrites.
The mix of elements in these meteorites suggests they must be the remnants of a large rocky body, a few hundred kilometers across, born near the terrestrial planets in the dusty disk that once swirled around our sun.
Then, in 2022, Morbidelli and colleagues showed that any of these enstatites that land on Earth today must come from a collection of bits and pieces in the asteroid belt between Mars and Jupiter. Those bits all broke off Athor, one of the many asteroids there, after it collided long ago with some other object in the belt. Altogether, that family of material adds up to an asteroid roughly 60 kilometers across — much smaller than the one thought to have birthed the enstatites in the first place. That means Athor must be only one piece of that larger rocky body, left over from a collision that destroyed it much closer to the sun.
“The question is, which dynamical mechanism can allow the implantation of Athor in the asteroid belt?” Morbidelli said at the meeting.
He tried computer simulations of several possibilities, but so far, only the giant planet instability seems capable of sending Athor to a stable orbit in the asteroid belt.
This couldn’t have happened earlier than 60 million years after the birth of the solar system, Morbidelli said. Radioactive elements in the enstatite chondrites indicate their parent body was slowly cooling until then, which means it was still large. It hadn’t yet collided with one of the many other planetesimals stirred around by the forming terrestrial planets.
On the other hand, simulations suggest the instability can’t have occurred later than about 100 million years after the solar system began. A study in 2018 concluded that if the giant planets migrated later, a pair of asteroids dubbed Patroclus-Menoetius, trailing Jupiter around the sun while orbiting each other, would have been pulled apart.
That 60-million- to 100-million-year window makes the instability a prime suspect in the diversion of a hypothesized planet that hit Earth, creating the moon (SN: 3/15/23). The timing “seems right,” says Matthew Clement, an astrophysicist at the Johns Hopkins Applied Physics Laboratory in Laurel, Md. “Lots of things were happening in the solar system’s early history. However, dynamically speaking, we don’t have a whole lot of reason to believe that things changed much after the moon-forming impact.”
But he cautions that Morbidelli’s estimate is based on “one data point, of the breakup of one asteroid, pieces of which serendipitously happened to get to Earth.”
Still, “it’s nice that [the new result] is actually based on some real data, even if it’s indirectly, rather than just computer models,” says planetary scientist John Chambers. He has questions, though. “They suggest this happened when the formation of the terrestrial planets was more or less complete, apart maybe from the giant impact that formed the moon,” says Chambers, of the Carnegie Institution for Science in Washington, D.C. “But then there’s a good chance it would have messed up the orbits of the terrestrial planets and possibly led to some of them colliding,” which the current lineup of planets suggests did not happen.
Both Chambers and Matthews have worked on scenarios in which the orbital instability occurred even earlier, just a few million years after the solar system began. That earlier time for the instability would help explain one of the outstanding riddles of the solar system: the relatively small size of Mars compared with Earth and Venus. That’s because the instability would have removed many objects from near the orbit of Mars before it could grow to the size of Earth or larger. The new result from Morbidelli’s team seems to exclude that solution.
“I’m prepared to rely on the evidence,” Chambers says. But he isn’t convinced yet because many facets of the solar system’s present structure must be reconciled with any date for the giant planet instability.
Clement agrees. “There’s problems if the instability happened at 500 million years. There’s still problems that we have to resolve if it happened when they say it happened,” he says. “And there’s still problems if it happened immediately after the planets formed, in the first few million years. This story is not done being told yet.” More
Maybe hold off on that Martian ice fishing trip. Two new studies splash cold water on the idea that potentially habitable lakes of liquid water exist deep under the Red Planet’s southern polar ice cap.
The possibility of a lake roughly 20 kilometers across was first raised in 2018, when the European Space Agency’s Mars Express spacecraft probed the planet’s southern polar cap with its Mars Advanced Radar for Subsurface and Ionosphere Sounding, or MARSIS, instrument. The orbiter detected bright spots on radar measurements, hinting at a large body of liquid water beneath 1.5 kilometers of solid ice that could be an abode to living organisms (SN: 7/25/18). Subsequent work found hints of additional pools surrounding the main lake basin (SN: 9/28/20).
But the planetary science community has always held some skepticism over the lakes’ existence, which would require some kind of continuous geothermal heating to maintain subglacial conditions (SN: 2/19/19). Below the ice, temperatures average –68° Celsius, far past the freezing point of water, even if the lakes are a brine containing a healthy amount of salt, which lowers water’s freezing point. An underground magma pool would be needed to keep the area liquid — an unlikely scenario given Mars’ lack of present-day volcanism.
“If it’s not liquid water, is there something else that could explain the bright radar reflections we’re seeing?” asks planetary scientist Carver Bierson of Arizona State University in Tempe.
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In a study published in the July 16 Geophysical Research Letters, Bierson and colleagues describe a couple other substances that could explain the reflections. Radar’s reflectivity depends on the electrical conductivity of the material the radar signal moves through. Liquid water has a fairly distinctive radar signature, but examining the electrical properties of both clay minerals and frozen brine revealed those materials could mimic this signal.
Adding weight to the non-lake explanation is a study from an independent team, published in the same issue of Geophysical Research Letters. The initial 2018 watery findings were based on MARSIS data focused on a small section of the southern ice cap, but the instrument has now built up three-dimensional maps of the entire south pole, where hundreds to thousands of additional bright spots appear.
“We find them literally all over the region,” says planetary scientist Aditya Khuller, also of Arizona State University. “These signatures aren’t unique. We see them in places where we expect it to be really cold.”
Creating plausible scenarios to maintain liquid water in all of these locations would be a tough exercise. Both Khuller and Bierson think it is far more likely that MARSIS is pointing to some kind of widespread geophysical process that created minerals or frozen brines.
While previous work had already raised doubts about the lake interpretation, these additional data points might represent the pools’ death knell. “Putting these two papers together with the other existing literature, I would say this puts us at 85 percent confidence that this is not a lake,” says Edgard Rivera-Valentín, a planetary scientist at the Lunar and Planetary Institute in Houston who was not involved in either study.
The lakes, if they do exist, would likely be extremely cold and contain as much as 50 percent salt — conditions in which no known organisms on Earth can survive. Given that, the pools wouldn’t make particularly strong astrobiological targets anyway, Rivera-Valentín says. (SN: 5/11/20).
Lab work exploring how substances react to conditions at Mars’ southern polar ice cap could help further constrain what generates the bright radar spots, Bierson says.
In the meantime, Khuller already has his eye on other areas of potential habitability on the Red Planet, such as warmer midlatitude regions where satellites have seen evidence of ice melting in the sun. “I think there are places where liquid water could be on Mars today,” he says. “But I don’t think it’s at the south pole.” More
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