Astronomers have witnessed the biggest explosion in space.
The explosive event labeled AT2021lwx has been observed to be ten times brighter than any known supernova, the explosions that occur when massive stars die. And while supernova explosions only last a few months, this explosive event has been raging for at least three years.
AT2021lwx is also three times brighter than the light emitted when stars are torn apart and devoured by supermassive black holes, events called “tidal disturbance events” or “TDEs.” The explosion is about 8 billion light-years from Earth and therefore occurred when the universe was only 6 billion years old.
AT2021lwx was first spotted by the Zwicky Transient Facility in California in 2020 and later recovered by the Hawaii-based Asteroid Earth Impact Last Warning System (ATLAS). Both of these systems are designed to monitor the night sky for astronomical events that change rapidly in brightness over time, also known as “transients”. This change in brightness may indicate a supernova or gamma-ray burst (GRB) deep in the universe or something much closer to home like a comet or asteroid.
Although spotted by these facilities three years ago, the scale and power of the AT2021lwx explosion was unknown until now.
“We stumbled upon it by chance as it was flagged by our search algorithm when we were looking for a type of supernova,” University of Southampton researcher Philip Wiseman, who led the search, said in a statement sent. by e-mail. “Most supernovae and TDEs only last a few months before fading away. For something to be bright for more than two years was immediately very unusual.”
Wiseman and the team of astronomers believe that AT2021lwx could be the result of a black hole violently disrupting a cloud of gas with a mass thousands of times that of the sun. In doing so, the black hole swallowed fragments of the gas cloud, sending shockwaves both into what remains of the gas and into a larger doughnut-shaped torus of dust surrounding it, causing them to emit a bright electromagnetic radiation.
Events like this have been observed before, they are rare. Also, none of those seen before have been scaled to AT2021lwx.
Although AT2021lwx is not as bright as the GRB 221009A gamma-ray burst spotted by astronomers in 2022, this event which erupted 2.4 billion light-years away lasted only ten hours after its detection. Even though that’s quite long for a GRB, it means that AT2021lwx emitted a lot more energy over its lifetime than this gamma-ray burst alone did.
Measuring the power of a cosmic explosion
After its initial discovery, the team of researchers behind this discovery continued to examine AT2021lwx using several different telescopes, including the Neil Gehrels Swift Telescope, the New Technology Telescope in Chile, and the Gran Telescopio Canarias. in La Palma, Spain.
Following these observations, the researchers took the spectrum of light emitted by the event and split it into its constituent wavelengths, measuring how light was emitted and absorbed around the event. This allowed the researchers to calculate the distance to the source of AT2021lwx.
“Once you know the distance to the object and its luminosity, you can calculate the luminosity of the object at its source,” said Sebastian Hönig, a member of the team and a professor at the University of Southampton, in the press release. “Once we did those calculations, we realized it was extremely brilliant.”
The only thing in the known universe that is as bright as AT2021lwx are supermassive black holes. When these black holes feed on stellar gas falling into them at high speed, they can emit incredibly bright emissions called quasars.
“With a quasar, we see the luminosity rise and fall over time,” added Mark Sullivan, team member and professor at the University of Southampton. “But looking back a decade, there was no detection of AT2021lwx, and then suddenly it appears with the brightness of the brightest things in the universe, which is unprecedented.”
Although there are other possible explanations for the explosive event, astronomers currently favor the explanation that an extremely large cloud of mostly gaseous hydrogen or dust was blown out of its orbit around the black hole and sucked into it. . This will not be definitively determined until the team has collected more data on AT2021lwx.
The team will now examine the explosion in different wavelengths of light, including X-rays. This could reveal the temperature of the event and the processes driving it. They will also run computer simulations to find out if their model of a titanic cloud of gas perturbed by a black hole could explain AT2021lwx.
“With new facilities, like the Vera Rubin Observatory’s Legacy Survey of Space and Time, coming online in the coming years, we hope to discover more events like this and learn more about them,” said Wiseman concluded in the statement. “It could be that these events, although extremely rare, are so energetic that they are key processes in how the centers of galaxies change over time.”
The team’s research is discussed in an article published in the journal Monthly Notices of the Royal Astronomical Society.
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