A team of astronomers led by the University of Southampton has uncovered the largest cosmic explosion ever witnessed.
In comparison to most supernovae, which are only visible for a few months, the AT2021lwx explosion has already lasted for over three years, making it the largest ever witnessed.
The explosion took place nearly eight billion light years away, when the universe was around six billion years old, and is still being detected by a network of telescopes.
AT2021lwx was first detected in 2020 by the Zwicky Transient Facility in California and subsequently picked up by the Asteroid Terrestrial-impact Last Alert System (ATLAS) based in Hawaii. Until now, the scale of the explosion had been unknown.
“We came upon this by chance, as it was flagged by our search algorithm when we were searching for a type of supernova,” said Dr Philip Wiseman, research fellow at the University of Southampton.
“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.”
The researchers believe that the explosion is a result of a vast cloud of gas that has been violently disrupted by a supermassive black hole. Fragments of the cloud would be swallowed up, sending shockwaves through its remnants, as well as into a large dusty ‘doughnut’ surrounding the black hole.
Such events are very rare and nothing on this scale has been witnessed before.
Last year, astronomers witnessed the brightest explosion on record: a gamma-ray burst known as GRB 221009A. While this was brighter than AT2021lwx, it lasted for just a fraction of the time, meaning the overall energy released by the AT2021lwx explosion is far greater.
“Looking back over a decade, there was no detection of AT2021lwx, then suddenly it appears with the brightness of the brightest things in the universe, which is unprecedented,” said Professor Mark Sullivan, also of the University of Southampton.
The team are now setting out to collect more data on the explosion, measuring different wavelengths, including X-rays which could reveal the object’s surface and temperature, and what underlying processes are taking place.
They will also carry out upgraded computational simulations to test if these match their theory of what caused the explosion.
“With new facilities, like the Vera Rubin Observatory’s Legacy Survey of Space and Time, coming online in the next few years, we are hoping to discover more events like this and learn more about them,” Wiseman added.
“It could be that these events, although extremely rare, are so energetic that they are key processes to how the centres of galaxies change over time.”
The findings of the research have been published in the journal Monthly Notices of the Royal Astronomical Society.
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