An unprecedented neutrino detection in the Mediterranean has pushed the boundaries of high-energy astrophysics, raising new questions about the most extreme processes in the universe.
Three years ago, scientists detected an “ultra-energetic” cosmic neutrino in the Mediterranean Sea, the most energetic ever recorded. The discovery drew global attention from researchers, the media, and the public. One reason for the intense interest is that the particle’s origin remains unknown. Its energy was more than ten times higher than that of any previously observed neutrino.
A study published in the Journal of Cosmology and Astroparticle Physics by the KM3NeT collaboration points to a possible explanation. The team operates the KM3NeT/ARCA detector off the coast of Sicily and suggests the particle may have come from a population of blazars. These are active galactic nuclei powered by supermassive black holes that shoot jets of plasma toward Earth.
A Diffuse Source Rather Than a Single Event
Bendahman and her colleagues found clues suggesting the neutrino did not come from a single dramatic event such as an explosion or flare. In such cases, scientists usually look for an electromagnetic “counterpart,” meaning a signal in radio, optical, X-ray, or gamma-ray wavelengths from the same region of the sky at the same time.
No such signal was detected for this event. “This does not completely rule out the possibility of a point-like source,” Bendahman says, “but it leads us to consider that our neutrino may come from a diffuse background that is, from a flux of neutrinos including contributions from many sources.”
