Underwater telescope detects highest energy neutrino ever
Astrophysicists have been searching for highly energetic cosmic particles called neutrinos for decades. Now, a telescope installed beneath the Mediterranean Sea has caught sight of the highest energy neutrino observed to date. This groundbreaking discovery, made possible with support from five EU-funded projects – KM3NET-INFRADEV2, MuSES, MessMapp, UNOS and ChETEC-INFRA – will help scientists gain better insight into the most energetic and distant events taking place in the universe. The high-energy neutrino – a tiny particle with barely any mass that can pass through entire planets unimpeded and undetected – was detected by the deep-sea Cubic Kilometre Neutrino Telescope, or KM3NeT, on 13 February 2023. The aptly nicknamed ghost particle carried 220 peta-electronvolts (PeV) of energy – about 100 million billion times the energy of visible light photons and roughly 30 times the highest neutrino energy detected until now. However, it took pouring through months of observations to realise its significance. “I first realized how spectacular it was when I looked at our event display,” remarks Paschal Coyle, a researcher at KM3NET-INFRADEV2 project coordinator and ChETEC-INFRA project partner French National Centre for Scientific Research, in a news item posted on ‘Astronomy’. “It had so many more photons (light particles) than anything we had ever seen,” adds Coyle, who is a co-author of the paper published in the journal ‘Nature’. The researchers were able to spot the ultra-high-energy neutrino thanks to the highly sensitive optical sensors on the KM3NeT’s ARCA detector installed at a depth of about 3 450 metres off the coast of Sicily in Italy. The ARCA array is one of the KM3NeT’s two detectors, with the second – ORCA – located offshore in Toulon, France.
Capturing the light
On 13 February, the ARCA detector picked up a signal from an extremely high-energy muon – a subatomic particle generated by a neutrino – streaking across it. Although the flash of light generated by the muon travelling through the water lasted only about 2 microseconds, the telescope captured the photons with microprecision. It was estimated that the muon had an energy of about 120 PeV, suggesting that the neutrino that produced it had an even higher energy of about 220 PeV. The neutrino’s energy and its almost horizontal direction are what makes this event particularly extraordinary. It takes extreme cosmic conditions such as an exploding star or supermassive black hole to create such a neutrino. “This neutrino is definitely in the energy range where we expect cosmogenic neutrinos to be,” Coyle comments. Studying such a neutrino could help scientists gain better insight into the cosmos. The team have identified a number of active galaxies from which the neutrino may have originated. However, none were confirmed as the source, and its origins remain uncertain. The UNOS (Unifying Neutrino Observatories Searches) project ended in 2024. KM3NET-INFRADEV2 (Towards full implementation of the KM3NeT Research Infrastructure) and ChETEC-INFRA (Chemical Elements as Tracers of the Evolution of the Cosmos - Infrastructures for Nuclear Astrophysics) end in 2025. MessMapp (Mapping Highly-Energetic Messengers throughout the Universe) ends in 2026 and MuSES (Multi-messenger Studies of Extragalactic Super-colliders) in 2029. For more information, please see: KM3NET-INFRADEV2 project MuSES project MessMapp project UNOS project ChETEC-INFRA project website
Keywords
KM3NET-INFRADEV2, MuSES, MessMapp, UNOS, ChETEC-INFRA, neutrino, particle, muon, KM3NeT, telescope
