Astronomers witness largest-ever explosion 8 Billion light years away from Earth

Astronomers have uncovered the largest cosmic explosion ever witnessed. The explosion, known as AT2021lwx, occurred nearly 8 billion light years away from Earth, when the universe was approximately 6 billion years old.

This explosion surpasses the brightness of any known supernova (a star that explodes) by more than tenfold and exceeds the brightness of the brightest tidal disruption event, where a star is consumed by a supermassive black hole, by threefold. According to the team, led by the University of Southampton astronomers, such events are very rare and nothing on this scale has been witnessed before.

In 2020, the Zwicky Transient Facility located in California detected AT2021lwx for the first time, followed by the Asteroid Terrestrial-impact Last Alert System (ATLAS) based in Hawaii. These cutting-edge facilities are designed to survey the night sky and identify transient objects that exhibit rapid changes in brightness, indicating cosmic events including supernovae, as well as tracking asteroids and comets.

The Southampton-led team conducted extensive investigations of AT2021lwx using multiple telescopes including the Neil Gehrels Swift Telescope, ESO's New Technology Telescope in Chile, and the Gran Telescopio Canarias in La Palma, Spain. The researchers successfully determined the distance to the object by examining the spectrum of light. This involved splitting the light into various wavelengths and carefully measuring the distinctive absorption and emission features within the spectrum.

"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 realised this is extremely bright," says Professor Sebastian Hönig from the University of Southampton, a co-author of the research.

According to the team, quasars - supermassive black holes characterized by a continuous influx of gas falling into them at high velocities - are the only objects in the universe that are as bright as AT2021lwx.

While several theories have been proposed regarding the cause of this massive explosion, the team led by Southampton believes that the most feasible explanation is an extraordinarily vast cloud of gas, consisting mostly hydrogen, or dust that has deviated from its regular orbit around the black hole and been sent flying in.

The team's findings are published in Monthly Notices of the Royal Astronomical Society.