The Oh-My-God particle was an ultra-high-energy cosmic ray detected on 15 October 1991 by the Fly's Eye camera in Dugway Proving Ground, Utah, United States.
The particle's energy was unexpected and called into question prevailing theories about the origin and propagation of cosmic rays.
is 938 MeV, this means it was traveling at 0.9999999999999999999999951 times the speed of light, its Lorentz factor was 3.2×1011 and its rapidity was 27.1.
Due to special relativity, the relativistic time dilation experienced by a proton traveling at this speed would be extreme.
If the proton originated from a distance of 1.5 billion light years, it would take approximately 1.71 days in the reference frame of the proton to travel that distance.
For the Oh-My-God particle hitting a nitrogen nucleus, this gives 2900 TeV, which is roughly 200 times higher than the highest collision energy of the Large Hadron Collider, in which two high-energy particles going opposite directions collide.
In the center-of-mass frame of reference (moving at almost the speed of light), the products of the collision, also moving apart at near light speed, would therefore have carried around 2900 TeV of total energy.
Although this amount is phenomenally large for a single elementary particle – far outstripping the highest energy that human technology can generate in a particle – it is still far below the level of the Planck scale, where exotic physics is expected.
The Oh-My-God particle had 1020 (100 quintillion) times the photon energy of visible light, equivalent to a 140-gram (5 oz) baseball travelling at about 28 m/s (100 km/h; 63 mph).
Its energy was 20 million times greater than the highest photon energy measured in electromagnetic radiation emitted by an extragalactic object, the blazar Markarian 501.
[8][needs update] While the particle's energy was higher than anything achieved in terrestrial accelerators, it was still about 40 million times lower than the Planck energy (1.2208901×1028 eV).
Particles of that energy would be required in order to expose effects on the Planck scale.
A proton with that much energy would travel 1.665×1015 times closer to the speed of light than the Oh-My-God particle did.
As viewed from Earth and observed in Earth's reference frame, it would take about 3.579×1020 years (2.59×1010 times the current age of the universe) for a photon to overtake a Planck energy proton with a 1 cm lead.
[citation needed] Since the first observation, hundreds of similar events (energy 5.7×1019 eV or greater) have been recorded, confirming the phenomenon.
More recent studies using the Telescope Array Project have suggested a source of the particles within a 20 degree radius "warm spot" in the direction of the constellation Ursa Major.
[3][10][11] The Amaterasu particle, named after the sun goddess in Japanese mythology, was detected in 2021 and later identified in 2023, using the Telescope Array observatory in Utah, United States.
[12] This particle appears to have emerged from the Local Void, an empty area of space bordering the Milky Way galaxy.
[13] It contained an amount of energy comparable to dropping a brick from the height of the waist.
No promising astronomical object matching the direction from which the cosmic ray arrived has been identified.