On February 13, 2023, an extraordinary cosmic event unfolded near Sicily, where a highly energetic muon raced nearly parallel to the horizon. This muon, traveling with an unprecedented energy of approximately 220 petaelectron volts (PEV), surpassed the highest energy cosmic neutrinos previously recorded by a factor of twenty. The muon was not an atmospheric particle but rather was generated by a neutrino originating from the vast expanse of space. This discovery has sparked excitement and intrigue within the scientific community, as the energy level of this neutrino reached an astounding 220 million billion electron volts.
The remarkable detection occurred at the Cubic Kilometre Neutrino Telescope (KM3NeT) situated in the Mediterranean Sea. Although still under construction, KM3NeT's sensitive sensors successfully captured the faint bluish light emitted by the muon as it traversed through the water. Previously, the record for the highest energy neutrino stood at around 10 PEV. This recent observation has set a new benchmark and poses compelling questions about the origins of such energetic particles.
Scientists remain uncertain about the precise source of this high-energy neutrino. However, Luigi Antonio Fusco, a physicist at the University of Salerno in Fisciano, Italy, suggests that most neutrinos originate from active galactic nuclei, which are luminous cores of galaxies fueled by supermassive black holes consuming gas and dust.
“Most of them are active galactic nuclei,” – Luigi Antonio Fusco
The expansion of KM3NeT promises to enhance its capacity to detect neutrinos and potentially trace their origins. In the region of the sky from which the neutrino emerged, twelve celestial objects have been identified as potential sources. KM3NeT comprises two neutrino detectors, one located off the coast of Sicily and the other near southern France. The ongoing data collection by KM3NeT's scientists is anticipated to continue over the next decade, providing more insights into these elusive particles.
Despite these advancements, theoretical physicist Kohta Murase from Penn State cautions against drawing definitive conclusions about the neutrino's origins due to the complexity involved in such determinations.
“The problem is that there are so many,” – Luigi Antonio Fusco
The detection of this unprecedented neutrino event has taken the scientific community by surprise. Luigi Antonio Fusco described it as a "shocking situation," comparing it to a scenario where "neutrino physicists have only ever seen fires fueled by a few sticks of kindling, and then someone comes with a flamethrower."
“It’s a kind of shocking situation,” – Luigi Antonio Fusco
“It’s like neutrino physicists have only ever seen fires fueled by a few sticks of kindling, “and then someone comes with a flamethrower.” – Luigi Antonio Fusco
In addition to KM3NeT's efforts, other neutrino telescopes are being developed to further explore these enigmatic particles. Notably, an expansion of the IceCube project is planned, and construction is underway for another observatory in the South China Sea. Erik Blaufuss expressed initial skepticism about the detection but acknowledged its significance.
“I definitely went in kind of skeptically,” – Erik Blaufuss
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