On February 13, 2023, a neutrino with record-breaking energy was captured by the KM3NeT underwater telescope, located off the coast of Sicily. This discovery, published in
Nature in February 2025, marks a major milestone in the study of the most violent cosmic phenomena, such as black holes or gamma-ray bursts.
Neutrinos, nearly elusive elementary particles, pass through matter without interacting with it. Their detection is a technological challenge, but their study provides valuable insights into extreme astrophysical events. This neutrino, with an energy of 220 peta-electronvolts (or 220 million billion electron-volts), opens a new window into the Universe.
Artistic view of the KM3NeT detector
© Camille Combes, Agence Ouvreboîte
Image Wikimedia Record energy for a tiny particle
With an energy thirty times greater than that of previously detected neutrinos, this neutrino challenges current astrophysical models. Its origin could be linked to violent cosmic phenomena, such as star explosions or supermassive black holes.
This detection was made possible by the KM3NeT telescope, submerged at a depth of 3,450 meters (11,319 feet). The telescope integrates light sensors, which recorded the Cherenkov light produced in a very rare interaction of the neutrino with water, and its superluminal speed in this medium.
KM3NeT: a state-of-the-art underwater observatory
The KM3NeT telescope, not yet fully completed, comprises two sites: ARCA, dedicated to high-energy neutrinos, and ORCA, specialized in low-energy neutrinos. These facilities exploit the properties of deep water to detect neutrinos with unmatched precision.
The marine environment offers ideal conditions: absence of stray light and water transparency. The sensors, anchored to the seabed, detect the light flashes produced by neutrinos, allowing the reconstruction of their trajectory and energy.
An origin still shrouded in mystery
Researchers are trying to trace the source of this neutrino, which could come from an extragalactic event. Blazars, supermassive black holes, or gamma-ray bursts are among the hypotheses being considered.
The analysis of the neutrino's direction and energy will help refine these hypotheses. This discovery could also shed light on the origin of cosmic rays, ultra-energetic particles whose source remains unknown.
A new era for neutrino astronomy
This detection marks the beginning of a new era for the study of neutrinos. KM3NeT, once fully completed, will allow for the observation of more of these particles and a better understanding of extreme cosmic phenomena.
Neutrinos, cosmic messengers, offer a unique view of the Universe. Their study, combined with that of gravitational waves and gamma rays, paves the way for multi-messenger astronomy.
To go further: What is a neutrino?
Neutrinos are elementary particles with no electric charge and almost no mass. Produced in nuclear reactions, such as those in the Sun or supernovas, they pass through matter with a very low probability of interaction, making them difficult to detect.
Their study helps us better understand extreme astrophysical processes. High-energy neutrinos, like the one detected by KM3NeT, are produced in violent cosmic events, such as black holes or gamma-ray bursts.
How are neutrinos detected?
The detection of neutrinos relies on the observation of Cherenkov light, produced when a neutrino interacts with an atomic nucleus in water or ice. This light is captured by networks of optical sensors, such as those in KM3NeT or IceCube in Antarctica.
Underwater or ice-embedded telescopes provide a sufficient detection volume to capture these extremely rare interactions. These installations require advanced technologies to operate in extreme environments.
Article author: Cédric DEPOND