Astronomers at Queen’s University Belfast have helped uncover the largest cosmic explosions in the universe.
An investigation led by the University of Southampton, in collaboration with Queen’s University Belfast, revealed an explosion more than 10 times brighter than any known supernova (exploding star). The explosion, known as AT2021lwx, has lasted more than three years. Most supernovae are only visibly bright for several months. The last one visible in our galaxy was seen from Earth in 1605.
The event that gave rise to AT2021lwx happened eight billion light years away, meaning it has taken the last eight billion years for that light to reach Earth.
What astronomers are witnessing is an event that took place long before the Sun or Earth formed. If an event like this was to occur in our galaxy, or our neighbouring galaxies, it would be so bright as to be visible during day time.
Last year, a team of researchers at Queens led by Michael Fulton also 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.
Matt Nicholl from Queen’s helped to analyse the brightness of the explosion. He described the discovery as “totally unprecedented” because astronomers were there at the birth of this event. One day they were looking at an immutable piece of sky, the next they saw this cosmically enormous object or, as he calls it, a monster black hole.
“At first, we thought this flare-up could be the result of a black hole consuming a passing star. But our models showed that the black hole would have to have swallowed up 15 times the mass of our Sun to stay this bright for this long,” said Dr Nicholl.
“Encountering such a huge star is very rare, so we think a much larger cloud of gas is more likely. Many massive black holes are surrounded by gas and dust and we are still trying to work out why this particular black hole started feeding so vigorously and so suddenly.”
Using the Asteroid Terrestrial-impact Last Alert System (Atlas) in Hawaii, the Queen’s University researchers led the search for cosmic explosions and were able to process and analyse huge amounts of data.
Vast cloud of gas
After detailed analysis, the researchers now believe that the explosion is a result of a vast cloud of gas, possibly thousands of times larger than our sun, 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.
In this latest discovery, astronomers at Queen’s worked through the enormous amount of images that these telescopes gathered. Atlas first spotted AT2021lwx back in November 2020 and has been observing it every few nights for the last 2½ years. The data shows that the explosion was nearly 100 times brighter than all the stars in our galaxy combined.
The findings of the research have been published today in Monthly Notices of the Royal Astronomical Society.