For over a decade, floating cranes have been lowering a strange cargo some 3000 metres under the Mediterranean Sea. The objects look otherworldly: large, shiny spheres crammed with electronics. They are, in fact, detectors for a machine called KM3NeT, designed to search for one of the most mysterious fundamental particles.
The machine is still several years from completion, so Paschal Coyle got quite a shock when, in 2023, he spotted a dramatic signal in its preliminary data. It was a neutrino, as expected, but one unlike anything ever seen before. “When I first tried looking at this event, my program crashed,” says Coyle, a physicist at the Centre for Particle Physics of Marseille, France.
KM3NeT had detected a neutrino from space that had about 35 times more energy than any previously seen. It was thousands of times more energetic than anything created in our best particle accelerators. Neutrinos have always defied easy understanding – they interact so faintly with other matter that their presence is normally all but imperceptible. That is behind the decision to place the project’s detectors at the bottom of the sea. But this one seemed almost impossible.
Now the race is on to work out what in the universe could have possibly produced it. As astronomers parse the details, it seems there are two possibilities, both of which point towards some of the deepest and strangest reaches of the cosmos. There is much at stake, as understanding this particle’s origins may help us grasp the true nature of neutrinos and reveal the…
