Deep-Sea Detector Identifies Blazars as Potential Source of Record-Breaking 220 PeV Ultra-High-Energy Neutrino

A KM3NeT study suggests the most energetic neutrino ever detected originated from blazars, proving these black holes are more powerful than once thought.

By: AXL Media

Published: Mar 9, 2026, 6:11 AM EDT

Source: The information in this article was sourced from Sissa Medialab

Forensic Investigation of a Deep Sea Cosmic Signal

On February 13, 2023, an extraordinary physical event occurred in the depths of the Mediterranean Sea that has since reshaped our understanding of cosmic accelerators. The KM3NeT/ARCA detector, submerged off the Sicilian coast, recorded the passage of a neutrino with an energy level of approximately 220 PeV. This value exceeds all previously recorded high-energy neutrinos by more than an order of magnitude, prompting an international scientific inquiry into its origin. Because the particle’s source was not immediately obvious, researchers from the KM3NeT collaboration adopted a forensic approach, simulating various cosmic scenarios to see which most accurately matched the rare, ultra-energetic trace left in the water.

The Role of Blazars as Extreme Particle Accelerators

The primary "suspect" in this cosmic mystery is a specific class of active galactic nuclei known as blazars. These are massive galaxies hosting supermassive black holes at their centers, characterized by powerful jets of plasma directed almost exactly toward Earth. The study suggests that these objects may act as a diffuse background source, contributing to a constant flux of high-energy particles rather than a single, isolated explosion. By simulating a population of these blazars using open-source AM3 software, the team, including lead researcher Meriem Bendahman, found that the physical parameters of these celestial bodies are consistent with the production of such "ultra-energetic" particles.

Modeling Baryonic Loading and Spectral Indices

To build a realistic model of how a blazar could produce a 220 PeV neutrino, the researchers focused on two critical variables: baryonic loading and the proton spectral index. Baryonic loading refers to the ratio of energy carried by protons compared to electrons, which directly dictates how many neutrinos are generated. The proton spectral index determines the likelihood of these particles reaching extreme, record-breaking energy levels. By adjusting these parameters within known physical constraints, such as magnetic field strength and emission region size, the team demonstrated that a population of blazars could account for the observed event without violating other known laws of astrophysics.