A team of astronomers led by the University of Southampton has revealed the largest cosmic explosion in history.
The explosion is ten times brighter than any known supernova (exploding star) and three times brighter than the brightest tidal disruption event, in which the 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 for a few months. They occurred about 8 billion light-years away, when the universe was about 6 billion years old, and are still being detected by a network of telescopes.
Researchers believe that the explosion was caused by a huge cloud of gas, possibly thousands of times more massive than our sun, which was severely disrupted by a supermassive black hole. Parts of the cloud will be swallowed up, sending shock waves through its remnants, as well as into a large, dusty “doughnut” that surrounds the black hole. Such events are very rare and nothing of this magnitude has ever been witnessed before.
Last year, astronomers witnessed the brightest explosion on record – a gamma-ray burst known as GRB 221009A. Although this was brighter than the AT2021lwx, it only lasted for a fraction of the time, which means that the total energy generated by the AT2021lwx’s explosion is much greater.
The results of the research were published today in Monthly Notices of the Royal Astronomical Society.
AT2021lwx was first detected in 2020 by the Zwicky Transit Facility in California, and was subsequently picked up by the Alert Ground Shock Alert System (ATLAS) in Hawaii. These facilities scan the night sky to detect transient objects that rapidly change in brightness indicating cosmic events such as supernovae, as well as find asteroids and comets. Until now, the size of the explosion is unknown.
“We came up with this quite by accident, as it was flagged by our search algorithm when we were looking for some kind of supernova,” says Dr Philip Wiseman, a research fellow at the University of Southampton, who led the research. “Most supernovae and tidal disturbance events only last a couple of months before fading. For something to be bright for two years or more was immediately unusual.”
The team investigated the object further using several different telescopes: the Neil Gehrels Swift Telescope (a collaboration between NASA, the United Kingdom, and Italy), the New Technology Telescope (operated by the European Southern Observatory) in Chile, and the Gran Telescope Canarias in Los Angeles. Palma, Spain.
By analyzing the spectrum of light, dividing it into different wavelengths and measuring the different absorption and emission properties of the spectrum, the team was able to measure the distance to the object.
says Professor Sebastian Honig of the University of Southampton, co-author of the research.
The only objects in the universe that are as bright as AT2021lwx are quasars – supermassive black holes with a continuous stream of gas falling on them at high speed.
Professor Mark Sullivan, also from the University of Southampton and another co-author on the paper, explains, “With a quasar, we see the brightness go up and down over time. But looking back over a decade, there was no detection of AT2021lwx, and then it suddenly appears with a bright The brightest objects in the universe, which is unprecedented.”
What caused the explosion?
There are various theories as to what caused such an explosion, but the Southampton-led team believes the most plausible explanation is an extremely large cloud of gas (mostly hydrogen) or dust that deviated from its path around the black hole. They were sent by plane.
The team is now setting out to collect more data about the explosion – measuring the different wavelengths, including X-rays, that can reveal the object’s surface and temperature, and what underlying processes are taking place. They will also run advanced computational simulations to test if they match their theory of the cause of the explosion.
Dr Philip Weissmann added, “With new facilities, such as the Vera Rubin Observatory’s Space and Time Legacy Survey, coming online in the next few years, we hope to discover more events like this and learn more about them. That could be these events, though.” From their extreme rarity, they are so energetic that they are fundamental processes of how the centers of galaxies change over time.”
P Wiseman et al, Multi-wavelength observations of the AT2021lwx accretion event, Monthly Notices of the Royal Astronomical Society (2023). DOI: 10.1093/mnras/stad1000. academ.oup.com/mnras/advance…ras / stad1000 / 7115325
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