The largest gamma ray explosion never observed was generated by collapse of a massive star. This is confirmed by James Webbwhose data was used by a team led by Northwestern University to find a supernova, i.e. the energetic explosion with which a star dies. The study, published on Nature Astronomyinvestigated the phases following theGRB event 221009A: This is the brightest gamma-ray burst (GRB) signal ever recorded, observed in 2022.
On October 9, 2022, Earth’s gamma-ray detectors were hit by the light of a powerful explosion that occurred about 2.4 billion light years from Earth, in the direction of the constellation Arrow. Lasting a few hundred seconds, the high-energy event was the brightest gamma-ray signal astrophysicists have witnessed.
Among the various space observatories that have detected it, also the NASA Fermi Gamma-ray Space Telescope and the Swift Observatory, both with a strong Italian contribution, both technological and in terms of software and data analysis, thanks to the fundamental role of Asy.
About six months after the detection, a team of researchers investigated the phases following the propagation of light with the James Webb, looking for clues as to what event had given rise to the immense explosion. The Webb near-infrared spectrograph, the instrument NirSpec, thus observed the characteristic signatures of elements such as calcium and oxygen, which are typically found within a supernova. Hence the confirmation that the origin of the GRB 221009A event is the collapse of a massive starfrom which the supernova now revealed was generated.
The surprise for astrophysicists was to find that the supernova that generated this great energetic event was not brighter than previous supernovae observed with much less powerful gamma ray signals.
“One might expect that the same collapsing star that produces a very energetic and luminous GRB would also produce a very energetic and luminous supernova. But it turns out that this is not the case. We have an extremely bright GRB, but a normal supernova,” he says Peter Blanchardfirst author of the research.
The star that generated the GRB 221009A event and the supernova now discovered by Webb turned out to be a rapidly rotating massive star. Astrophysicists hypothesize that the explosion of these particular stars, in addition to the fusion of neutron stars, could be the events generating the heaviest elements in the universe.
«Different elements absorb and emit photons at different wavelengths, depending on their atomic structure, giving each element a unique spectral signature – says Peter Blanchard. – Examining the spectrum of the largest gamma-ray burst, we did not see any signatures of heavy elements, which suggests that extreme events like GRB 221009A are not primary sources. This is crucial information to continue trying to understand where the heaviest elements form.”
Despite having discovered the origin of the largest gamma ray explosion ever observed, the research still leaves open the picture of the mechanisms that produce elements heavier than iron in the cosmos.
Featured image: Artist’s impression of GRB 221009A showing the narrow relativistic jets emerging from a central black hole that gave rise to the signal and the expanding remnants of the original star ejected through the supernova explosion. Credit: Aaron M. Geller / Northwestern / CIERA / IT Research Computing and Data Services
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