Gamma-ray bursts are luminous phenomena caused by the most powerful explosions that occur in the universe, at least since the Big Bang. Flashes of light that in a handful of seconds release the amount of energy that our Sun will release in its entire life. The most powerful ever observed from Earth is known by the acronym GRB 221009A, it hit our atmosphere on October 9, 2022 and since then it continues to reveal new surprises. The latest comes from an international research led by Radboud University, which involved the National Institute for Astrophysics, the Gran Sasso Science Institute and the National Institute for Nuclear Physics: it contained an energetic peak, or more precisely an “emission line”, which reached 12 million electron volts, a feature never observed before, in over 50 years of research.
“A few minutes after the gamma-ray burst began, NASA’s Fermi satellite recorded an unusual feature that caught our attention,” explains Maria Edvige Ravasio of Radboud University and INAF, who led the study. “I didn’t expect to find a spike in energy,” Ravasio continues, “and when I realized that what I was seeing was real and not the product of an error in the analysis, it was exciting.”
To put these energy values into perspective, consider that the energy of visible light emitted by our Sun reaches just 2-3 electron volts. As the authors of the new study, just published in Science, explain, a power of 12 million electron volts is so high that it is not predicted by standard models of gamma-ray burst production, and therefore requires the formulation of new hypotheses to be explained.
The most likely, according to the authors of the study, is that it is a phenomenon of annihilation between matter and antimatter: electrons and positrons produced in some cosmic event of unimaginable power must have collided, destroying each other, transforming into other particles and producing an incalculable amount of energy. “When an electron and a positron collide, they cancel each other out and produce a pair of gamma rays with an energy of 0.511 MeV,” explains Gor Oganesyan, a researcher at the Gran Sasso Science Institute and the Gran Sasso National Laboratories of the INFN who participated in the study. “Since the jet, where the matter moves almost at the speed of light, points towards us, this emission is pushed towards higher energies.”
Events like GRB 221009A, produced about 2.4 billion light years from Earth, are generated by violent cosmic phenomena, such as the merger of a neutron star with a twin or with a black hole, or the collapse of a massive star. Phenomena during which enormous relativistic jets of energy are produced (enormous, extremely powerful plasma emissions), within which the particles of matter and antimatter described in the new study could have been produced. A discovery that could mark an important step forward in the understanding of gamma-ray bursts.