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a day ago
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A star may have survived partial black hole spaghettification
When a star strays too close to a supermassive black hole, extreme gravitational forces ravage it, shredding and stretching it into spaghetti. The term for this gruesome process is actually "spaghettification," according to NASA, inspired by Stephen Hawking's book, A Brief History of Time. In it, the late theoretical physicist first described what would happen to a person approaching a black hole's "event horizon" — its point of no return — in space. Astronomers used to think this was an immediate death sentence for a star. Now an international team, led by Tel Aviv University in Israel, has published the first confirmed case of a star surviving such a brush, only to return 700 days later for another go. The findings, which appear in The Astrophysical Journal Letters, don't contradict the concept of spaghettification but show that it could be a repeatable process for some stars, said Iair Arcavi, who supervised the research. "A star isn't a uniform ball of matter," Arcavi told Mashable. "The inner part is more dense, and the outer part is more 'fluffy.' So the outer part is more easily spaghettified. If the star kept to some distance from the black hole, it could avoid the denser parts from getting spaghettified, too." Black holes are some of the most inscrutable phenomena in the universe. They are regions in space where gravity is so intense that nothing, not even light, can escape. About 50 years ago, they were little more than a theory — a kooky mathematical solution to a physics problem. Even astronomers at the top of their field weren't entirely convinced they existed. Today, not only are black holes accepted science, they're getting their pictures taken by a collection of enormous, synced-up radio dishes on Earth. Humanity got a clear view of Sagittarius A*, the black hole at the center of the galaxy, for the first time in 2022. Last year, Tel Aviv University researchers spotted a tidal disruption event (TDE) near the center of a galaxy about 400 million light-years away using the Las Cumbres Observatory, a network of robotic telescopes around the world, designed to keep a close eye on rapid cosmic events. These TDEs are bright flares that occur when a black hole is destroying a star. What shocked them was that the flare was almost identical to another that occurred two years earlier, called AT 2022dbl, from the exact same location. After analyzing the data, scientists ruled out other explanations, like unrelated flares or gravitational lensing, and concluded that the same star was partially torn apart twice. Typically, when a star is pulled toward a black hole, its near side is stretched and pulled in while the far side is flung out. The resulting stream of gas and debris spirals around the black hole as it falls in — sort of like water circling a bathtub drain. These bursts of energy can outshine an entire galaxy, briefly illuminating the hidden black hole lurking at the heart of a galaxy. Over the past decade, astronomers have observed dozens of these flares. But one thing has perplexed them: Based on computer simulations, most of these events seem kind of weak. Previously, scientists had assumed the discrepancy between real and virtual flares has been due to knowledge gaps or the limitations of computer models. But AT 2022dbl's repeating flare may offer a simpler explanation. The star may not have been completely annihilated on its first trip around the black hole. Then, like a masochist, it returned roughly two years later to be damaged again. The study suggests it's possible many of these flares, once thought the calling cards of stellar death, aren't necessarily fatal events. The question now is whether this particular star is finally dead or if it'll be back again next year for more abuse. Either way, Arcavi said, astronomers will have to rethink these flares and what they say about the monsters lying in wait. Solve the daily Crossword
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6 days ago
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This star escaped a supermassive black hole's violent grips — then returned for round 2
When you buy through links on our articles, Future and its syndication partners may earn a commission. A distant supermassive black hole may have bitten off more than it can chew! Not only did the star it selected for a stellar meal escape its clutches, but it came back for a second encounter! Evidence of the death-defying star was spotted in the form of a flare that was followed by a near-identical second flare around two years later (700 days). The double-flare has been given the designation AT 2022dbl. The team behind this research ruled out the possibility that it was caused by two stars being devoured by this black hole, leaving them to conclude the flares came from two "bites" of the same stellar snack. The discovery is the first evidence of a star escaping a destructive encounter with a supermassive black hole and then coming back to let it take a second bite. The big question is, did the star survive to return for a second rematch with the black hole? It could therefore change our view of so-called "tidal disruption events" or "TDEs" in which black holes rip apart stars and devour their remains, indicating this could just be the first act of a longer cosmic performance. Some black holes prefer a lighter meal Supermassive black holes with masses equal to that of millions or billions of suns dwell at the heart of all large galaxies. TDEs occur when unfortunate stars wander too close to these cosmic titans and experience their immense gravitational influence. This generates terrific tidal forces within the star that simultaneously squash it horizontally while stretching it vertically. This process, vividly known as "spaghettification," results in shredded stellar pasta, some of which falls around the black hole, wrapping around it like spaghetti around a fork, and is gradually fed to it. The rest of this material is blasted out from around the supermassive black hole. The material that remains swirls around the black hole at incredibly speeds, generating friction that causes bursts of light, and the ejected material also flares. These flares last weeks to months, illuminating the region around the supermassive black hole, allowing it to be studied. However, over the last decade, some TDEs have been observed that don't behave the way scientists would expect. That is because both the temperature and brightness of some TDEs have been lower than expected. AT 2022dbl could explain this by implying that some black holes like to savour their stellar meals rather than immediately and totally destroying them. The team now wants to know if the third time is the charm for this daring star. If it survived its second black hole encounter, the star will swoop back toward the black hole, causing a third flare around 700 days after the second. "The question now is whether we'll see a third flare after two more years, in early 2026," team member and Tel Aviv University researcher Iair Arcavi said in a statement. "If we see a third flare, it means that the second one was also the partial disruption of the star. "So maybe all such flares, which we have been trying to understand for a decade now as full stellar disruptions, are not what we thought." Related Stories: — New kind of pulsar may explain how mysterious 'black widow' systems evolve — Hear 'black widow' pulsar's song as it destroys companion —NASA X-ray spacecraft reveals secrets of a powerful, spinning neutron star Should a third flare not erupt in two years, it would indicate that the star's second encounter with the black hole was fatal. Should this be the case, the similarity between the first flare and the second one would imply that non-fatal and fatal TDE flares, or partial and full disruptions, look the same. That is something that scientists had previously predicted but have never evidenced with observations. "Either way, we'll have to rewrite our interpretation of these flares and what they can teach us about the monsters lying in the centers of galaxies," Arcavi concluded. The team's research was published on July 1 in the Astrophysical Journal Letters.
