Astronomers said Friday they had identified the “largest” cosmic explosion ever observed, a fireball 100 times the size of our solar system that suddenly exploded in the distant universe more than three years ago. While astronomers presented what they believe is the most likely explanation for the explosion, they stressed that more research is needed to understand this mysterious phenomenon.

Dubbed AT2021lwx, the explosion isn’t the brightest flare observed in the universe. That record is still held by October’s gamma-ray burst, nicknamed BOAT as the brightest of all time. Philip Wiseman, an astrophysicist at the University of Southampton in the UK and lead author of the new study, said the AT2021lwx is considered the “biggest” explosion because it has released much more energy than the short BOAT burst in the past three years.

Wiseman told AFP it was an “accidental discovery”. The AT2021lwx was first detected by the Zwicky Transient Facility in California during an automated sky survey in 2020. But it was “basically in the database,” until people noticed it the following year, Wiseman said. But when astronomers, including Weizman, looked at it with more powerful telescopes, they realized what they had.

By analyzing the different wavelengths of light, they concluded that the explosion occurred about eight billion light-years away. It’s much further away than many other new bursts of light in the sky, which means the explosion behind it must have been much more powerful. According to Wiseman, it is about two trillion times brighter than the Sun.

Astronomers have considered several possible explanations. First, AT2021lwx is an exploding star, but the flare is 10 times brighter than any supernova seen before.

Another possibility is something called a tidal disruption event, where a star breaks apart while being absorbed by a supermassive black hole. But the AT2021lwx is still three times brighter than these events, and Wiseman said their research did not show that aspect. Similarly, the only bright cosmic event is a quasar, where supermassive black holes absorb large amounts of gas at the center of galaxies.

But Wiseman said they tend to flicker in brightness, whereas the AT2021lwx suddenly started flashing from scratch three years ago and still keeps flashing.

“This is something we’ve never seen before — it just popped up,” Wiseman said.

“The Absolute Puzzle”

In a new study published in the journal Monthly Notices of the Royal Astronomical Society, an international team of researchers has revealed what they believe is the most likely scenario. Their theory is that a single huge gas cloud – about 5,000 times the size of the Sun – is slowly being swallowed up by a supermassive black hole.

However, Wiseman said, “there is never certainty in science.” The team is working on new simulations to see if their theory is “totally plausible.” One problem may be that supermassive black holes lie at the center of galaxies – for an explosion of this size, a galaxy as large as the Milky Way could be expected, Wiseman said. However, no one has been able to detect a galaxy near AT2021lwx.

“It’s an absolute mystery,” Wiseman admitted.

Now that astronomers know what to look for, they’re scanning the sky to see if other similar eruptions have gone unnoticed.