Astronomers detect largest cosmic explosion ever seen

The event has currently lasted over three years, compared to most supernovae, which are only visibly bright for a few months

Astronomers have uncovered the largest cosmic explosion ever witnessed, which has currently lasted over three years. Image for Representation. | Photo Credit: Reuters

Astronomers say they have uncovered the largest cosmic explosion ever witnessed, which has currently lasted over three years.

The explosion, known as AT2021lwx, 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, the researchers said.

The explosion is more than ten times brighter than any known supernova or exploding star and three times brighter than the brightest tidal disruption event, where a star falls into a supermassive black hole, they said.

The event has currently lasted over three years, compared to most supernovae, which are only visibly bright for a few months, according to the resaerchers.

"We came upon this by chance, as it was flagged by our search algorithm when we were searching for a type of supernova," said Philip Wiseman, Research Fellow at the University of Southampton, who led the research published in the journal Monthly Notices of the Royal Astronomical Society.

"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," Wiseman said in a statement.

The team believes that the explosion is a result of a vast cloud of gas, possibly thousands of times larger than the 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.

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.

AT2021lwx was first detected in 2020 by the Zwicky Transient Facility in California, US, and subsequently picked up by the Asteroid Terrestrial-impact Last Alert System (ATLAS) based in Hawaii.

These facilities survey the night sky to detect transient objects that rapidly change in brightness indicating cosmic events such as supernovae, as well as finding asteroids and comets.

However, the scale of the explosion has been unknown until now.

There are different theories as to what could have caused such an explosion, but the team believes the most feasible explanation is an extremely large cloud of gas (mostly hydrogen) or dust that has come off course from its orbit around the black hole and been sent flying in.

The researchers 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.