Oh-My-God particle
The Oh-My-God particle was an ultra-high-energy cosmic ray detected on the evening of 15 October 1991 over Dugway Proving Ground, Utah, by the University of Utah's Fly's Eye Cosmic Ray Detector. Its observation was a shock to astrophysicists (hence the name), who estimated its energy to be approximately 3×1020 eV or 3×108 TeV. This is 20,000,000 times more energetic than the highest energy measured in electromagnetic radiation emitted by an extragalactic object and 1020 (100 quintillion) times the energy of visible light. Therefore, the particle was an atomic nucleus with a kinetic energy of 48 joules, equivalent to a 142 g (5 oz) baseball travelling at about 26 m/s (94 km/h; 58 mph).
This particle had so much kinetic energy it was travelling at ~ 99.999,999,999,999,999,999,999,510% of the speed of light. As a result, its Lorentz factor was ~ 3.2×1011. This is so near the speed of light that if a photon were travelling with the particle, it would take over 215,000 years for the photon to gain a 1-centimeter lead.
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