Fly's Eye Logged 320 Exaelectronvolt Cosmic Ray in 1991, Still Highest Ever Detected
Updated
Updated · spacedaily.com · Jul 25
Fly's Eye Logged 320 Exaelectronvolt Cosmic Ray in 1991, Still Highest Ever Detected
3 articles · Updated · spacedaily.com · Jul 25
Summary
51 joules in one particle—estimated at 320 exaelectronvolts—made the 1991 Fly’s Eye event in Utah the highest-energy cosmic ray ever recorded, a distinction it still holds more than three decades later.
Fly’s Eye did not capture the primary particle directly; it reconstructed the event from ultraviolet fluorescence produced when an atmospheric collision triggered an extensive air shower, with the original estimate carrying a ±90 exaelectronvolt uncertainty.
47 million times an LHC proton’s per-particle energy, the event showed nature can concentrate far more energy into a single particle than human accelerators, even though collider physics differs because the atmospheric target was nearly stationary.
About 100 million light-years is the rough upper travel distance if the particle was a proton, because interactions with the cosmic microwave background should drain energy from ultra-high-energy cosmic rays over longer journeys.
No source has been identified: magnetic fields can deflect charged particles, the primary may have been a proton or heavier nucleus, and later detections above 10^20 electronvolts confirm a rare population whose origins remain unresolved.