A groundbreaking discovery has rocked the field of neutrino astronomy—scientists have detected an ultra-high-energy neutrino using the KM3NeT telescope, with an energy level 16,000 times greater than the most powerful collisions at the Large Hadron Collider.
These elusive “ghost particles” provide a rare glimpse into the universe’s most extreme events, potentially originating from supermassive black holes or cataclysmic supernovae. The detection of this neutrino, possibly a cosmogenic one, could unlock new secrets about cosmic ray acceleration and the fundamental forces shaping our cosmos. However, more detections are needed to pinpoint its true origin and confirm its significance.
Chasing Ghost Particles
On February 13, 2023, an international team of scientists, including astronomers from the Max Planck Institute for Radio Astronomy in Bonn, detected a neutrino with record-setting energy using the KM3NeT telescope. This deep-sea observatory, spanning a kilometer in size, captured a signal 16,000 times more energetic than the most powerful particle collisions ever produced at CERN’s Large Hadron Collider.
How KM3NeT Captures Neutrinos
Neutrinos are among the most elusive particles in the universe. They have almost no mass, carry no electric charge, and rarely interact with matter. “They are special cosmic messengers that reveal the secrets of the most energetic phenomena in the universe,” said Rosa Coniglione, then deputy spokesperson for KM3NeT.
Because neutrinos pass through most matter undetected, KM3NeT relies on seawater as its detection medium. Soon, the observatory will span several cubic kilometers, dramatically increasing its sensitivity. When a high-energy neutrino interacts with an atomic nucleus in the water, it can produce a muon—a heavier cousin of the electron that carries a negative charge. The muon travels so fast that it generates a cone of light, known as Cherenkov radiation, similar to the sonic boom produced by a supersonic jet.
KM3NeT is designed to detect this light. The telescope consists of 230 vertical strings, each holding 18 spherical optical modules, resembling pearls on a necklace. Inside each module, 31 photomultipliers amplify even the faintest flashes of light from all directions. These instruments allow scientists to track the elusive neutrinos and uncover their origins, shedding light on some of the most powerful cosmic events in the universe.
A New Era for Neutrino Astronomy
KM3NeT is now detecting neutrinos from extreme astrophysical events, exploring previously uncharted energy ranges. “This first detection of a neutrino in the hundreds of PeV range opens a new chapter in neutrino astronomy,” says Paschal Coyle, KM3NeT spokesperson at the time of the detection and a researcher at IN2P3/CNRS in France. One petaelectronvolt (PeV) corresponds to 1015 or one quadrillion electronvolts.
Where Did the Record-Breaking Neutrino Come From?
The central question is where the high-energy particles that hit the Earth and react in its ocean or atmosphere come from.
“By adding observations from other telescopes, we seek to connect the acceleration of cosmic rays, the production of neutrinos, and the role of supermassive black holes in shaping these energetic phenomena,” says Yuri Kovalev of the Max Planck Institute for Radio Astronomy.
In addition to the environment of supermassive black holes, supernova explosions are also among the candidates for powerful cosmic particle accelerators. The high-energy neutrino that has now been measured could come directly from such an accelerator, or it could be the first detection of a cosmogenic neutrino.
Cosmogenic neutrinos could be produced when other cosmic particles react with the weak light of the cosmic microwave background, creating extremely energetic neutrinos. However, since only a single event has been measured here at hundreds of PeV, the origin remains uncertain. To learn more, researchers need to detect more such events.
High-Energy Particles from Space Are Nothing New
A somewhat smaller neutrino telescope of the same design, Antares, has also measured high-energy neutrinos from space. And there are a number of other creative experiments that have captured the particle bombardment from space. Such as the Pierre Auger Observatory in Argentina, which also measures Cherenkov radiation. In this case, however, the initiators among the cosmic particles are protons that hit the Earth’s atmosphere and trigger cascades of secondary particles in it. The muons that are created in the process are not detected in seawater, but in over 1600 water tanks distributed throughout the Argentinean pampas.
Explore Further:
- A Deep-Sea Telescope Just Detected the Most Energetic Ghost Particle Ever
- A 220 PeV Neutrino Shatters Records, Opening a New Window Into the Cosmos
Reference: “Observation of an ultra-high-energy cosmic neutrino with KM3NeT” by The KM3NeT Collaboration, 12 February 2025, Nature.
DOI: 10.1038/s41586-024-08543-1
A Global Collaboration to Uncover Cosmic Mysteries
The KM3NeT Collaboration is a large international effort involving more than 360 scientists, engineers, technicians, and students from 68 institutions across 22 countries. Together, they are working to detect and study neutrinos—tiny, elusive particles that can reveal powerful cosmic events.
Two Deep-Sea Detectors, One Mission
KM3NeT operates two deep-sea neutrino detectors: ARCA (Astroparticle Research with Cosmics in the Abyss), located off the coast of Sicily, and ORCA (Oscillation Research with Cosmics in the Abyss), near Toulon, France. ARCA is designed to study high-energy neutrinos and consists of 230 vertical detection units, each about 700 meters tall and spaced 100 meters apart. ORCA, optimized for studying neutrino properties, has 115 units, each 200 meters tall with 20-meter spacing.
Each detection unit holds 18 spherical optical modules, and each module contains 31 photomultipliers capable of detecting faint flashes of light produced by neutrino interactions. Data from both detectors are transmitted via submarine cables to shore stations: the INFN Laboratori Nazionali del Sud in Portopalo di Capo Passero, Italy, and the Laboratoire Sous-marin Provence Méditerranée in La Seyne-sur-Mer, France.
German Contributions to the Discovery
Several institutions in Germany played key roles in the study that led to the discovery of the record-breaking neutrino. These include:
- Friedrich-Alexander-Universität Erlangen-Nürnberg, with contributors M. Chadolias, Y. Darras, A. Domi, T. Eberl, T. Gal, N. Geißelbrecht, R. Gracia, K. Graf, C. Haack, L. Hennig, O. Kalekin, U.F. Katz, C. Kopper, R. Lahmann, J. Schnabel, J. Schumann, B. Setter, H. Warnofer, and S. Weissbrod
- Max Planck Institute for Radio Astronomy, with Y.Y. Kovalev, A. Plavin, and E. Ros
- Julius-Maximilian University of Würzburg, with S. Buson (also affiliated with DESY), M. Lincetto, and L. Pfeiffer
MuSES: A New Frontier in Cosmic Exploration
The MuSES project (Multi-messenger Studies of Energetic Sources) is a pioneering research initiative focused on understanding Active Galactic Nuclei (AGN)—some of the universe’s most powerful natural particle accelerators. Supported by the European Research Council (ERC) through the European Union’s Horizon Europe research and innovation programme (grant agreement No. 101142396), MuSES plays a vital role in connecting neutrino observations with other cosmic signals.
