Astronomers said Friday they have identified the “largest” cosmic explosion ever observed, a fireball 100 times the size of our solar system that suddenly began flaring up in the distant universe more than three years ago.
While astronomers have provided what they believe is the most likely explanation for the outburst, they stress that more research is needed to understand this puzzling phenomenon.
The explosion, called AT2021lwx, is not the brightest flash ever observed in the universe. This record is still held by a gamma-ray burst in October dubbed BOAT – for the brightest of all time.
Philip Wiseman, an astrophysicist at Britain’s University of Southampton and lead author of a new study, said that AT2021lwx was considered the largest explosion because over the past three years it released much more energy than the short BOAT flash produced.
“It’s an accidental discovery,” Weizmann told AFP.
AT2021lwx was first detected by Zwicky’s transit facility in California during an automated sky survey in 2020.
But Wiseman said it was “basically in a database” until humans noticed it the following year.
It was only when astronomers, including Weismann, looked at it through more powerful telescopes that they realized what they had in store for them.
By analyzing the different wavelengths of light, they determined that the explosion was about eight billion light-years away.
This is much further away than most other flashes of light in the sky – which means the explosion left behind must have been much larger.
It’s estimated to be about two trillion times brighter than the Sun, Weismann said.
Astronomers have considered several possible explanations.
One is that AT2021lwx is an exploding star – but the flash is 10 times brighter than any “supernova” previously seen.
Another possibility is a so-called tidal disruption event, when a star is torn apart when it is sucked into a supermassive black hole. But AT2021lwx is still about three times brighter than those events, and Wiseman said their research didn’t point in that direction.
The only bright cosmic event that’s somewhat comparable is a quasar, when supermassive black holes guzzle massive amounts of gas at the center of galaxies.
They tend to flicker in brightness, Wiseman said, whereas the AT2021lwx suddenly started blazing out of nothing three years ago, and it still glows away.
“This thing we’ve never seen before — it just came out of nowhere,” Wiseman said.
“the ultimate puzzle”
In the new study published in Monthly Notices of the Royal Astronomical SocietyThe international team of researchers put together what they believe is the most likely scenario.
Their theory is that a single huge cloud of gas – about 5,000 times more massive than the Sun – is slowly being consumed by a supermassive black hole.
But Wiseman said 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”.
One problem could be that supermassive black holes are at the centers of galaxies — for an explosion of this size, a galaxy the size of the Milky Way would be expected, Weizmann said.
But no one has been able to detect a galaxy near AT2021lwx.
“This is an absolute mystery,” Wiseman admitted.
Now that astronomers know what to look for, they are looking up at the sky to see if other similar bursts have been missed.
P Wiseman et al, Multi-wavelength observations of the AT2021lwx accretion event, Monthly Notices of the Royal Astronomical Society (2023). DOI: 10.1093/mnras/stad1000. academ.oup.com/mnras/advance…ras / stad1000 / 7115325
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