High-energy particles constantly rain down on Earth, but scientists have recently detected a groundbreaking event: a neutrino from deep space with an energy far exceeding anything previously observed.
On February 13, 2023, an undersea detector near Sicily recorded a record-breaking neutrino event. The particle's energy was estimated at an astonishing 220 petaelectronvolts (PeV), dwarfing the previous record of just 10 PeV.
Only a few astronomical objects, such as supernovae or black holes, can accelerate particles to such extreme energies. One possible source is a blazar—an active supermassive black hole emitting a jet of radiation almost directly at Earth.
Given the unprecedented energy level, it might also be the first-ever detected cosmogenic neutrino, originating from cosmic rays interacting with photons from the background radiation left over from the Big Bang.
Neutrinos are elementary particles with no electric charge and a nearly zero mass. Billions pass through us every second, but they rarely interact with matter, making them difficult to detect. Detection requires a large volume of water or ice, monitored by thousands of detectors for flashes of light from neutrino interactions.
The record-breaking neutrino was detected by a Cubic Kilometer Neutrino Telescope (KM3NeT) array, located 3,450 meters below the Mediterranean Sea. The array's 378 modules, each with 31 light-sensitive detectors, watch for the elusive neutrino flash.
During the 2023 event, over 28,000 photons were detected as particles produced by the neutrino's passage streaked across the detector. The particles traveled almost horizontally, indicating the neutrino journeyed through rock and water in Earth's crust before reaching the KM3NeT.
The light originated from another elementary particle, a muon, produced during cascading interactions. This muon had an estimated energy of around 120 PeV, remarkably high for such particles, but nothing compared to its parent particle.
The team explored four hypotheses regarding the neutrino's source: within our galaxy, outside but still in the local Universe, a transient event like a gamma-ray burst, or from a distant galaxy. The direction did not match the first three possibilities, leaving extragalactic sources as the likely origin, potentially involving active supermassive black holes like blazars.
Researchers searched the sky region for blazars responsible for this neutrino, identifying 12 candidates. However, none of these associations are definitive, and further investigations are necessary.
Another possibility is cosmogenic neutrino production, where high-energy particles result from cosmic rays interacting with the cosmic microwave background or intergalactic light. If confirmed, this would be the first documented detection of such a neutrino.
Continued research will be essential to unravel the mystery surrounding this record-breaking neutrino and its origins.
