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.
