A neutrino with more energy than we’ve ever seen before was picked up by a detector on the floor of the Mediterranean Sea, and it seems to have a distant cosmic origin
By Alex Wilkins
12 February 2025
Part of the KM3NeT neutrino detector on the seafloor
KM3NeT
A shockingly powerful neutrino that ripped through a new particle detector in the Mediterranean Sea has taken physicists by surprise, and it could be a first tantalising glimpse into some of the universe’s most cataclysmic events, such as the merging of supermassive black holes.
Neutrinos, sometimes referred to as “ghost particles”, barely interact with most matter because they are nearly massless and have no electric charge. This means that neutrino detectors typically incorporate vast amounts of dense substance, such as water or ice, in the hopes that a powerful neutrino might knock into an atom and produce a shower of particles that reveal tell-tale signs of its existence.
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Damien Dornic at the Centre for Particle Physics of Marseille in France and his colleagues have done just that, spotting the most energetic neutrino ever seen. The team used the cubic kilometre neutrino telescope (KM3NeT), a pair of detector arrays at the bottom of the Mediterranean Sea, which picked up the neutrino on 13 February 2023. The detector was only 10 per cent complete at the time, so it took Dornic and his team by surprise.
“First, we were confused,” he says. “When we realised more and more that this event is truly exceptional, we were really excited.”
The signal looked promising, showing up as a nearly horizontal bright line in the detector. The researchers think this was created by small, electron-like particles called muons that were produced in the wake of the neutrino slamming through the detector and gave off light that KM3NeT’s detectors could pick up.