A fireball 100 times larger than the solar system and 2 trillion times brighter than the sun was discovered more than three years ago. Scientists are trying to unravel the cause of the explosion, which is an “absolute mystery” like never before. Astronomers announced Friday (12/05) that they’ve located the largest cosmic explosion ever observed, a ball of energy 100 times larger than the solar system. The explosion, which has been dubbed AT2021lwx, is not the brightest ever seen in the universe. That record is still held by a gamma-ray burst in October, dubbed BOAT (short for “brightest ever”). Philip Wiseman, an astrophysicist at the University of Southampton in the UK, explained that AT2021lwx was considered the “greatest” cosmic explosion because it released so much more energy than BOAT released in its short flash. Weizmann told Agence France-Presse that the discovery of the new explosion was accidental. The Zwicky Transient Facility astronomical observing project in California, US, first detected AT2021lwx during an automated sky survey in 2020. But it “basically sat in a database” until humans noticed it the following year, he said. Weismann, lead author of a new study on the cosmic explosion. Only when he and other astronomers analyzed the fireball through more powerful telescopes did they realize the potential of what they were observing. They estimated the explosion to be about 8 billion light-years from Earth. That is, much further away than most other flashes of light in the sky – which means that the explosion behind the flare must be much larger. According to Weizmann, astronomers estimate that AT2021lwx is 2 trillion times brighter than the sun. The team now wants to gather more data about the explosion, measuring different wavelengths, including X-rays, which can reveal the object’s surface and temperature. Possible causes of the explosion Astronomers are working with several possible explanations for the Big Bang. One is that AT2021lwx is a supernova – a powerful, luminous starburst – even though the brightness it emits is 10 times brighter than any previously observed supernova. Another possibility is a so-called tidal disruption event, an astronomical phenomenon that occurs when a star is torn apart by being sucked into a supermassive black hole. But AT2021lwx is still about three times brighter than those events, and Wiseman says his research doesn’t point in that direction. The only comparable bright cosmic event is a quasar, when supermassive black holes devour massive amounts of gas at the center of galaxies. But this phenomenon often has a flicker glow, while the AT2021lwx suddenly exploded three years ago and is still burning. “This thing we’ve never seen before — it just came out of nowhere,” Wiseman said. In the new study, published in Monthly Notices of the Royal Astronomical Society, the international team of researchers lays out what they believe is the most likely scenario. Their theory is that one huge cloud of gas – about 5,000 times more massive than the Sun – is slowly being consumed by a supermassive black hole. But Wiseman recalls that “in science, there is no absolute certainty.” He added that the team is working on new simulations to see if their theory is “completely plausible”. The problem with this hypothesis, the astronomer said, is that supermassive black holes lie at the center of galaxies — and for an explosion of this size, the galaxy would have to be the size of the Milky Way. But it was unable to locate a galaxy near AT2021lwx. “This is an absolute dilemma,” Weizmann admitted. Now that astronomers know what to look for, they’re scanning the skies to see if science hasn’t missed other similar explosions. ek (AFP, DPA, EFE) 
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