Astronomers have witnessed the largest explosion in space.

The explosive event labeled AT2021lwx was observed to be ten times brighter than any known supernova, the explosions that occur as massive stars die. And whereas supernova explosions only last a few months, this explosive event has been raging for at least three years.

AT2021lwx is also three times brighter than the light that is emitted as stars are ripped apart and devoured by supermassive black holes, occurrences called “tidal disruption events” or “TDEs.” The blast is around 8 billion light-years from Earth and thus occurred when the universe was just 6 billion years old.

AT2021lwx was first spotted by the Zwicky Transient Facility in California in 2020 and was then picked up by the Asteroid Terrestrial-impact Last Alert System (ATLAS) based in Hawaii. Both of these systems are designed to survey the night sky for astronomical events that rapidly change in brightness over time, also known as “transients.” This change in brightness can indicate a supernova or a gamma-ray burst (GRB) deep in the universe or something much closer to home like a comet or an asteroid.

Though it was spotted by these facilities three years ago, the sheer scale and power of the explosion AT2021lwx were unknown until now.

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