Oh-My-God particles - NASA balloon just launched to investigate them

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Lorenzo von Matterhorn
Jan 31, 2009
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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.[1][2] Its observation was a shock to astrophysicists (hence the name), who estimated its energy to be approximately 3×10^20 eV or 3×10^8 TeV. This is 20,000,000 times more energetic than the highest energy measured in electromagnetic radiation emitted by an extragalactic object[3] and 10^20 (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 ~ 99.999999999999999999999510% of the speed of light. As a result, its Lorentz factor was ~ 3.2×10^11. 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.

The energy of this particle is some 40,000,000 times that of the highest energy protons that have been produced in any terrestrial particle accelerator. However, only a small fraction of this energy would be available for an interaction with a proton or neutron on Earth, with most of the energy remaining in the form of kinetic energy of the products of the interaction. For the Oh-My-God particle, this gives 7.5×10^14 eV, roughly 60 times the collision energy of the Large Hadron Collider.[5]

Ultra-high-energy cosmic ray


In astroparticle physics, an ultra-high-energy cosmic ray (UHECR) is a cosmic ray particle with a kinetic energy greater than 1×1018 eV, far beyond both the rest mass and energies typical of other cosmic ray particles.

An extreme-energy cosmic ray (EECR) is an UHECR with energy exceeding 5×10^19 eV (about 8 joule), the so-called Greisen–Zatsepin–Kuzmin limit (GZK limit). This limit should be the maximum energy of cosmic ray particles that have traveled long distances (about 160 million light years), since higher-energy ray particles would have lost energy over that distance due to scattering from photons in the cosmic microwave background. It follows that EECR could not be survivors from the early universe but are cosmologically "young", emitted somewhere in the Local Supercluster by some unknown physical process.

These particles are extremely rare; between 2004 and 2007, the initial runs of the Pierre Auger Observatory (PAO) detected 27 events with estimated arrival energies above 5.7×10^19 eV, i.e., about one such event every four weeks in the 3000 km2 area surveyed by the observatory.

EUSO-SPB To Detect Cosmic Rays From Above By Looking Down

Ultra-High Energy Cosmic Rays (UHECRs) from the farthest reaches of space are extremely rare, entering the Earth’s atmosphere at a rate of just one per one square-kilometer of area per century. To unravel the mysteries associated with these cosmic rays, enter NASA’s super pressure balloon and the pioneering Extreme Universe Space Observatory (EUSO) instrument. Learn more from Principal Investigator Angela Olinto about how EUSO, flying 110,000 feet (33.5 kilometers) above the ground on a balloon, will look downward to detect these high-energy cosmic rays by observing fleeting moments of UV fluorescence over a broad swathe of the Earth’s atmosphere.



Two takeaways so far:
At 60x the energy of the LHC, nothing to fear from the LHC then. Apparently we get hit by these OMG particles all the time - relatively speaking.
These must originate somewhere close since their extreme velocity wouldn't make it far across space.

What would be the time dilation that this particle would experience? Nearly stopped I assume. With the Lorentz contraction, what would be the relative length in it's direction of travel?