Neutrinos are nearly massless particles that pass through ordinary matter almost unimpeded, which makes them notoriously hard to detect. Halzen's design used that difficulty as a starting point: IceCube watches for the Cherenkov effect, a flash of blue light emitted when charged particles such as muons move through ice faster than light itself travels in that medium. By tracking those flashes, the detector can trace a neutrino's path back to its source.

That approach gave astronomers a new way to observe violent events across the universe. In 2017, IceCube detected neutrinos carrying energies in the hundreds of peta-electronvolts, far beyond anything produced by the Large Hadron Collider. The findings pointed to blazars, galaxies with supermassive black holes that fire off jets of particles at speeds close to that of light, as a likely source of the highest-energy neutrinos reaching Earth.

Last year, the KM3NeT detector in the Mediterranean independently confirmed IceCube's observations, giving the blazar findings a second detector's backing. That confirmation strengthened the case for multimessenger astronomy, the practice of combining neutrino detections with gamma-ray and gravitational-wave data to build a fuller picture of cosmic events. The Vera Rubin Observatory in Chile has added another layer to that work, using AI to cross-reference alerts from different instruments so astronomers can move quickly to follow up on phenomena as they're detected.