To understand everything, you have to go back in time at lightning speed. On October 9, 2022, astronomers detected a gigantic flare of gamma rays, the most intense form of electromagnetic radiation. This flash of light of record energy reached Earth last year after a two billion light-year journey across the cosmos. And this distant traveler disrupted the upper layers of the atmosphere in an unprecedented way, according to a study published this Tuesday.
This phenomenon was caused by the most extreme events in the Universe, such as the explosions of giant stars. This gamma-ray burst nicknamed BOAT (“Brightest Of All Time”), emitted at a distance of about two billion light years, illuminated telescopes for only seven minutes, but left a residual light visible to amateur astronomers for seven hours.
The upper ionosphere affected
The powerful lightning activated lightning detectors in India, and triggered instruments dedicated to studying solar flares. Scientists were quickly able to determine its impact on long-wave radio communications in the lower part of the ionosphere (the upper layer of the Earth’s atmosphere), between 60 and 350 km altitude.
By continuing to analyze the phenomenon, Italian and Chinese researchers observed, for the first time, that it had also affected the upper part of this same ionosphere. Located between 350 and 950 km above Earth, near the edge of space, the upper ionosphere is where radiation from the Sun transforms into charged particles that form a large electric field.
“A form” previously “never observed”
For around twenty years, experts have debated the possibility that gamma-ray bursts could affect the upper ionosphere, explains Mirko Piersanti, lead author of the study published in Nature Communications. “I think we have finally answered this question,” commented this researcher at the Italian University of L’Aquila.
A stroke of luck for his team: the Sino-Italian CSES satellite, equipped with an electric field detector, was “exactly in the zone illuminated by the gamma-ray burst”, 500 km above the Earth. “We found a shape in the electric field never observed before,” specifies the researcher. “It’s incredible, we can see things that happen in deep space but also affect the Earth,” said Erik Kuulkers, gamma ray expert at the European Space Agency (ESA), in a press release.
“Completely erase” the ozone layer
The discovery should help understand the potential threat from future gamma-ray bursts. The worst-case scenario would be for such a powerful eruption to occur in our galaxy, the Milky Way. It would have the power to “completely erase” the Earth’s ozone layer, explains Mirko Piersanti. Everything on the surface would then be exposed to the Sun’s ultraviolet rays, which could wipe out life on Earth. But don’t panic because it is just as likely that the ionosphere absorbs all the gamma rays and that “nothing happens” for Earthlings, continues the researcher.
The BOAT gamma-ray burst that occurred last year in our sky from the small constellation Arrow, officially called GRB 221009A, could come either from the explosion of a massive star at the end of its life, or from the birth of a black hole . Or both, given its power: a giant star explodes and becomes a supernova, before collapsing in on itself and forming a black hole. Matter then forms a disk around the black hole, is absorbed there and released in the form of energy. On average, more than one gamma-ray burst hits Earth every day, but a burst of BOAT’s intensity is estimated to occur only once every 10,000 years.