Astronomers reveal the biggest cosmic explosion ever seen

May 12, 2023

(Nanowerk News) A team of astronomers led by the University of Southampton has uncovered the largest cosmic explosion ever.

The explosion is ten times brighter than any known supernova and three times brighter than the brightest tidal disturbance event, in which a star falls into a supermassive black hole.

The explosion, known as AT2021lwx, has currently lasted more than three years, compared to most supernovae which only appear bright for a few months. It happened nearly 8 billion light years away, when the universe was about 6 billion years old, and is still detectable by telescope networks. Artist’s impression of black hole accretion. (Image: John A. Paice)

Researchers believe the explosion was the result of an enormous cloud of gas, possibly thousands of times larger than our sun, which had been crushed by the supermassive black hole. The cloud fragments would be swallowed up, sending shockwaves through the remnants, and become a huge dusty ‘donut’ that surrounds the black hole. Such events are extremely rare and nothing has ever been witnessed before on this scale.

Last year, astronomers witnessed the brightest explosion on record – a burst of gamma rays known as GRB 221009A. While it’s brighter than the AT2021lwx, it only lasts a fraction of the time, meaning the overall energy released by the explosion of the AT2021lwx is much greater.

The results of the research were published in Monthly Notices of the Royal Astronomical Society (“Multi-wavelength observations of the extraordinary accretion event AT2021lwx”).


AT2021lwx was first detected in 2020 by the Zwicky Transient Facility in California, and then captured by the Hawaii-based Asteroid Terrestrial-impact Last Alert System (ATLAS). The facility surveys the night sky to detect transient objects that rapidly change in brightness indicating cosmic events such as supernovae, and finds asteroids and comets. Until now the scale of the explosion is unknown.

“We found this by chance, as indicated by our search algorithm when we searched for the type of supernova,” said Dr Philip Wiseman, Research Fellow at the University of Southampton, who led the research. “Most supernova events and tidal disturbances only last for a few months before dissipating. For something that’s been rosy for two plus years it immediately becomes pretty unusual.

The team investigated the object further with several different telescopes: the Neil Gehrels Swift Telescope (a collaboration between NASA, UK and Italy), the New Technology Telescope (operated by the European Southern Observatory) in Chile, and the Gran Telescopio Canarias in La Palma, Spain.

Measuring explosion

By analyzing the spectrum of light, dividing it into different wavelengths and measuring the different absorption and emission features of the spectrum, the team was able to measure the distance to objects.

“Once you know the distance to the object and how bright it is to us, you can calculate the object’s brightness at the source. After we did the calculations, we realized that it was very bright,” said Professor Sebastian Hönig from the University of Southampton, a co-author of the study.

The only things in the universe that are as bright as AT2021lwx are quasars – supermassive black holes with a constant stream of gas falling on them at great speed.

Professor Mark Sullivan, also from the University of Southampton and another co-author of the paper, explained: “With quasars, we see brightness flickering over time. But looking back over a decade with no detection of AT2021lwx, then suddenly appearing at an unprecedented brightness, the brightest object in the universe.”

What caused the explosion?

There are different theories as to what could cause such an explosion, but the Southampton-led team believes the most likely explanation is an enormous cloud of gas (mostly hydrogen) or dust erupting from its orbit around the black hole. and been sent flying in.

The team now set out to collect more data about the explosion – measuring different wavelengths, including X-rays that can reveal the surface and temperature of objects, and what processes underlay them. They will also perform enhanced computational simulations to test whether this matches their theory of the cause of the explosion.

Dr Philip Wiseman added: “With new facilities, such as the Vera Rubin Observatory’s Time and Space Heritage Survey, coming online in the next few years, we hope to discover more events like this and learn more about them. It could be that these events, although very rare, are so energetic that they are a key process in how the galactic center changes over time.

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