Largest Explosion Ever Seen Is an 8B-Year-Old Mystery

In 2020, a bright light appeared in the night sky. That light, still visible with advanced telescopes today, represents the largest explosion ever seen. You're forgiven for not noticing as this is all happening some 8 billion light years away, though that wasn't clear initially. The light was first detected automatically in 2020, but it was a year before astronomers observed the data, and another year before a team calculated the distance of the explosion. "We thought, 'Oh my God, this is outrageous!'" team lead Dr. Philip Wiseman of the University of Southampton tells the BBC. The distance showed the blast, occurring some 8 billion years ago, was incredibly bright—10 times brighter than any recorded supernova and three times brighter than a tidal disruption event, when a star is ripped apart and swallowed by a supermassive black hole, per Space.com.

And it remained so years after it was first detected. As the BBC notes, "there was nothing in the scientific literature that could account for something that was so bright that lasted so long." The event, dubbed AT2021lwx—described in Monthly Notices of the Royal Astronomical Society—isn't as bright as the brightest explosion on record, a 2022 gamma-ray burst from 2.4 billion light-years away known as GRB 221009A, but that burst only lasted a little over 10 hours. Supernova events generally last only a couple of months. "For something to be bright for two plus years was immediately very unusual," says Wiseman. And for something to appear suddenly "with the brightness of the brightest things in the universe" is "unprecedented," says team member Mark Sullivan, also of the University of Southampton.

Researchers are carrying out a number of tests to gain more data, including clues about the temperature of the explosion. But for now, they suspect a huge gas cloud, perhaps thousands of times bigger than our sun, was sucked into a supermassive black hole at the center of a distant galaxy, sending shockwaves across space and triggering bright electromagnetic radiation. Such events have been witnessed before, though never at this scale, per Space.com. According to Wiseman, "it could be that these events, although extremely rare, are so energetic that they are key processes to how the centers of galaxies change over time." Researchers plan to test this theory against computer simulations while looking for other huge explosions, which the most advanced telescopes, introduced within the next few years, should be able to detect. (More space stories.)