Astronomers Identify the Largest-Ever Cosmic Explosion

The burst is ten times brighter than any known exploding star and has lasted for more than three years

Black hole
Illustration of a black hole pulling in surrounding gas. John A. Paice under CC BY 4.0

Astronomers have spotted the largest cosmic explosion on record. The event, called AT2021lwx, is ten times brighter than any known exploding star—or supernova—and has lasted for more than three years. 

“We’ve estimated it’s a fireball 100 times the size of the solar system with a brightness about 2 trillion times the sun’s,” Philip Wiseman, an astronomer at the University of Southampton in England, tells the Guardian’s Hannah Devlin. “In three years, this event has released about 100 times as much energy as the sun will in its ten-billion-year lifetime.”

The flare was spotted by two systems that survey the night sky looking for objects with rapid shifts in brightness: California’s Zwicky Transient Facility first detected it in 2020, and then it was found by the Asteroid Terrestrial-impact Last Alert System in Hawaii.

“We came upon this by chance, as it was flagged by our search algorithm when we were searching for a type of supernova,” Wiseman says in a statement. “Most supernovae and tidal disruption events only last for a couple of months before fading away. For something to be bright for two plus years was immediately very unusual.”

Astronomers continued investigating the explosion from telescopes in Spain, Chile and low-Earth orbit. Their calculations indicated that the burst happened nearly eight billion light-years away from Earth, when the universe was around six billion years old.

The team was mystified by such a huge event, thinking at first it was a black hole eating a star. But models indicated the “black hole would have to have swallowed up to 15 times the mass of our sun to stay this bright for this long,” Matt Nicholl, an astrophysicist at Queen’s University Belfast in Northern Ireland who helped analyze the ongoing explosion, tells the New York Times’ Dennis Overbye. Such a large star is very rare, Wiseman tells the Guardian

Another possible explanation was a quasar, the brightest, most powerful class of objects in the known universe. Quasars are large emissions of energy from a supermassive black hole at the center of a galaxy. But this didn’t fit either—there didn’t seem to be a galaxy around AT2021lwx or any record of previous quasar activity, per the Times.

Now, researchers believe the explosion was caused by a black hole shredding a massive cloud of gas, sending shockwaves across space and leaving behind a “large dusty doughnut-shaped formation,” per the statement. The team published their findings in Monthly Notices of the Royal Astronomical Society.

Astronomers recently reported the brightest explosion on record, a gamma-ray burst termed the BOAT, or the “brightest of all time.” But that event was much shorter, observed for a little more than ten hours. For this newly reported explosion to have been so bright for so long, it must have released far more energy than the BOAT did, per the Guardian.

Scientists are now working on collecting more data, including observing AT2021lwx in different wavelengths, which may help reveal its temperature, reports BBC News’ Pallab Ghosh. They’re also on the lookout for other massive explosions. 

“We’ve never seen anything like this before and certainly not on this scale,” Robert Massey, the deputy executive director of the Royal Astronomical Society, tells the publication. “I’d be amazed if this is the only object like this in the universe.”

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