On October 9, 2022, a team of astronomers used the Fermi Gamma-ray Space Telescope to detect one of the largest cosmic explosions ever identified. It had occurred 1.9 billion light-years away and lasted about ten hours. It was baptized with the not-so-stellar name GRB 221009A and is recognized as one of the closer and more energetic bursts. At that time its brightness was such that it was also detected by amateur astronomers.
Now a new explosion has taken away the first place. A team of astronomers led by the University of Southampton has been able to see an explosion 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 been visible for more than three years, compared to most supernovae, which are only visibly bright for a few months. It took place almost 8 billion light-years away… and still is being detected by a telescope networks. AT2021lwx was first detected in 2020, but until Phillip Wiseman’s team published the results in the Monthly Notices of the Royal Astronomical Society, the magnitude of the explosion was unknown.
“We came across this by chance, as our search algorithm pointed it out when we were looking for a type of supernova,” Wiseman explains in a statement. Most supernovae and tidal disruption events only last a couple of months before fading out. Let something be bright during more than two years is very unusual”. By analyzing the spectrum of the light, dividing it into different wavelengths, and measuring the different absorption and emission characteristics 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 origin. When we made those calculations, we realized that it is extremely bright”, adds Sebastian Hönig, co-author of the study.
What caused the explosion?
There are different theories as to what could have caused such an explosion, but Wiseman’s team believes that the most likely explanation is an extremely large cloud of gas (mainly hydrogen) or dust that has been blown out of its orbit around the black hole. The team now sets out to collect more data on the explosion, measuring different wavelengths, including X-rays that could reveal the surface and temperature of the object, and what underlying processes are taking place. They will also carry out enhanced computer simulations to test whether they match their theory of the cause of the explosion.
“With new facilities, such as 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,” Wiseman concludes. It could be that these events, while extremely rare, are so energetic that they are key processes of how the centers of galaxies change over time«.
As our detection technology advances, the universe shows us stranger, brighter, or more explosive events, and what we thought we knew is expanding…just like the universe.
