A single atomic nucleus hit Utah with the force of a pitched baseball

On the evening of October 15, 1991, the University of Utah's Fly's Eye detector at Dugway Proving Ground recorded a single subatomic particle arriving from space with an energy of about 3.2×10²⁰ electronvolts - an atomic nucleus carrying the kinetic energy of a baseball traveling 100 kilometers per hour. Astrophysicists were so shocked they named it the Oh-My-God particle. Its energy was some 40 million times that of the most powerful protons ever produced in any particle accelerator on Earth.

At least fifteen similar events have been recorded since, confirming that ultra-high-energy cosmic rays are real and rare: the Pierre Auger Observatory in Argentina, with a detection area the size of Rhode Island, catches roughly one event above the highest energy thresholds every four weeks - particles at these extremes arrive at a rate of about one per square kilometer per century.

Where they come from is still unknown. They don't correlate with the plane of our galaxy, and galactic magnetic fields aren't strong enough to accelerate anything to such energies, so the sources must be extragalactic. The candidates physicists have proposed include magnetars - young neutron stars with the strongest stable magnetic fields in the observed universe - and the supermassive black holes at the centers of active galaxies.

Previously:

• Antarctic detector captured 13 radio pulses from cosmic rays in ice

• NASA says "something weird is going on" with the cosmos

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