Evrim Yazgin
Cosmos science journalist
NASA’s Fermi Telescope has revealed new details about the brightest of all time gamma-ray burst which may help explain these extreme and mysterious cosmic events.
Gamma-ray bursts (GRBs) usually last less than a second. They originate from the dense remains of a dead giant star’s core, called a neutron star. But what causes neutron stars to release huge amounts of energy in the form of gamma radiation is still a mystery.
In October 2022, astronomers detected the largest gamma-ray burst ever seen – GRB 221009A. It came from a supernova about 2.4 billion light years away. The event had an intensity at least 10 times greater than any other GRB detected. It was dubbed the BOAT, for brightest of all time.
Now, analysis of the data from that event has revealed the first emission line which can be confidently identified in 50 years of studying GRBs.
The new analysis is published in Science.
Emission lines are created when matter interacts with light. Energy from the light is absorbed and reemitted in ways characteristic to the chemical make up of the matter which is interacting with it.
When the light reaches Earth and is spread out like a rainbow in a spectrum, the absorption and emission lines appear. Emission lines appear as dimmer or even black lines in the spectrum, whereas emission lines are brighter features.
At higher energies, these features in the spectrum can reveal processes between subatomic particles such as matter and anti-matter annihilation which can produces gamma rays.
“While some previous studies have reported possible evidence for absorption and emission features in other GRBs, subsequent scrutiny revealed that all of these could just be statistical fluctuations,” says coauthor Om Sharan Salafia at the Italian National Institute of Astrophysics Brera Observatory in Milan. “What we see in the BOAT is different.”
The emission line appeared almost 5 minutes after the burst was detected. It lasted about 40 seconds.
It peaked at 12 million electron volts of energy – millions of times more energetic than light in the visible spectrum.
The astronomers believe the emission line was caused by the annihilation of electrons and their anti-matter counterparts, positrons. If their interpretation is correct, it means the particles would have to have been moving toward Earth at 99.9% the speed of light.
“After decades of studying these incredible cosmic explosions, we still don’t understand the details of how these jets work,” says Elizabeth Hays, Fermi project scientist at NASA’s Goddard Space Flight Center in the US. “Finding clues like this remarkable emission line will help scientists investigate this extreme environment more deeply.”
