The Largest Cosmic Explosion on Record Discovered

Saturday - May 13 2023, 14:45 UTC - 1 year ago

University of Southampton led team of astronomers discovered the largest cosmic explosion ever witnessed, with an emission of energy of more than ten times that of any supernova, resulting from a supermassive black hole violently disrupting a massive gas cloud at a distance of 8 billion light years.

Astronomers have discovered the largest cosmic explosion ever observed, AT2021lwx, which is believed to have been caused by a supermassive black hole violently disrupting a massive gas cloud. This explosion has released far more energy than any previous event due to its extended duration.

A team of astronomers led by the University of Southampton have uncovered the largest cosmic explosion ever witnessed.

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

The explosion, known as AT2021lwx, has currently lasted over three years, compared to most supernovae which are only visibly bright for a few months. It took place nearly 8 billion light years away, when the universe was around 6 billion years old, and is still being detected by a network of telescopes.

The researchers 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.

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.

The findings of the research were published today (Friday, May 12, 2023) in Monthly Notices of the Royal Astronomical Society.

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. 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. Until now the scale of the explosion has 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," says Dr. Philip Wiseman, Research Fellow at the University of Southampton, who led the research. "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 team investigated the object further with several different telescopes: the Neil Gehrels Swift Telescope (a collaboration between NASA, the UK, and Italy), the New Technology Telescope (operated by the European Southern Observatory) in Chile, and the Gran Telescopio Canarias in La Palma, Spain.

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

"Once you know the distance to the object and how bright it appears to us, you can calculate the brightness of the object at its source. Once we’d performed those calculations, we realized this is extremely bright," says Professor Ed.