Oh-My-God particle

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, U.S. It is the highest-energy cosmic ray ever observed.[1][2][3] The particle's energy was unexpected and called into question theories of that era about the origin and propagation of cosmic rays.

Not to be confused with the "God Particle", a nickname for the Higgs boson.

Comparisons

The Oh-My-God particle's energy was estimated as (3.2±0.9)×1020 eV, or 51±14 J. Although this amount is phenomenally large – far outstripping the highest energy that human technology can generate – it is still far below the level of the Planck scale, where exotic physics is expected.

Comparison to a photon

The Oh-My-God particle had 1020 (100 quintillion) times the photon energy of visible light, equivalent to a 142-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.[4]

Comparison to a proton

Assuming it was a proton, the particle was traveling at 0.9999999999999999999999951 times of the speed of light, its Lorentz factor was 3.2×1011 and its rapidity was 27.1. At this speed, if a photon were travelling alongside the particle, it would take over 215,000 years for the photon to gain a 1 cm lead, as seen from the Earth's reference frame. 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 from the reference frame of the proton to travel that distance.

The energy of this particle was some 40 million 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. The effective energy available for such a collision is [5] where E is the particle's energy and m c2 is the mass-energy of the assumed proton. For the Oh-My-God particle, this gives 7.5×1014 eV, which is roughly 60 times higher than the highest collision energy of the Large Hadron Collider (as of 2015).[6][7]

High energy, but far below the Planck scale

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. 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.

What is the highest energy particle possible?

The highest energy particle possible is an Ultra-high-energy cosmic ray which is a proton that travels at 99.99999999999999999998% the speed of light. However, these particles are extremely rare. Between 2004 and 2007, only 27 events were recorded and observed.

Later similar events

Since the first observation, hundreds of similar events (energy 5.7×1019 eV or greater) have been recorded, confirming the phenomenon.[8][9] These ultra-high-energy cosmic ray particles are very rare; the energy of most cosmic ray particles is between 107 eV and 1010 eV.

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][9][10]

See also

References
  1. Bird, D.J.; Corbato, S.C.; Dai, H.Y.; Elbert, J.W.; Green, K.D.; Huang, M.A.; Kieda, D.B.; Ko, S.; Larsen, C.G.; Loh, E.C.; Luo, M.Z.; Salamon, M.H.; Smith, J.D.; Sokolsky, P.; Sommers, P.; Tang, J.K.K.; Thomas, S.B. (March 1995). "Detection of a cosmic ray with measured energy well beyond the expected spectral cutoff due to cosmic microwave radiation". The Astrophysical Journal. 441: 144. arXiv:astro-ph/9410067. Bibcode:1995ApJ...441..144B. doi:10.1086/175344. S2CID 119092012.
  2. "The Fly's Eye (1981-1993) – The highest energy particle ever recorded". cosmic-ray.org.
  3. Wolchover, Natalie (14 May 2015). "The particle that broke a cosmic speed limit". Quanta Magazine. ISSN 2640-2661.
  4. Aharonian, F.; et al. (The HEGRA Collaboration) (1999). "The time averaged TeV energy spectrum of Mkn 501 of the extraordinary 1997 outburst as measured with the stereoscopic Cherenkov telescope system of HEGRA" (PDF). Astronomy & Astrophysics. 349: 11–28. arXiv:astro-ph/9903386v2. Bibcode:1999A&A...349...11A. S2CID 15448541.
  5. Lebedev, V.; Shiltsev, V. (May 29, 2014). Accelerator Physics at the Tevatron Collider. Springer. p. 1. ISBN 9781493908851. Retrieved June 3, 2019.
  6. Jowett, John (November 2015). "Lead-ion collisions: The LHC achieves a new energy record". CERN Bulletin.
  7. Nerlich, Steve (June 13, 2011). "Oh-My-God particles". Universe Today – via phys.org.
  8. Abdul Halim, A.; Abreu, P.; Aglietta, M.; Allekotte, I.; Allison, P.; Almeida Cheminant, K.; Almela, A.; Alvarez-Muñiz, J.; Ammerman Yebra, J.; Anastasi, G. A.; Anchordoqui, L.; Andrada, B.; Andringa, S.; Aramo, C.; Araújo Ferreira, P. R. (February 1, 2023). "A Catalog of the Highest-energy Cosmic Rays Recorded during Phase I of Operation of the Pierre Auger Observatory". The Astrophysical Journal Supplement Series. 264 (2): 50. doi:10.3847/1538-4365/aca537. ISSN 0067-0049.
  9. Abbasi, R. U.; Abe, M.; Abu-Zayyad, T.; Allen, M.; Anderson, R.; et al. (July 14, 2014). "Indications of intermediate-scale anisotropy of cosmic rays with energy greater than 57 EeV in the northern sky, measured with the surface detector of the Telescope Array Experiment". The Astrophysical Journal. 790 (2): L21. arXiv:1404.5890. Bibcode:2014ApJ...790L..21A. doi:10.1088/2041-8205/790/2/L21. eISSN 1538-4357. ISSN 0004-637X. S2CID 118481211.
  10. Cho, Adrian (8 July 2014). "Physicists spot potential source of 'Oh-My-God' particles". Science. doi:10.1126/article.22871. eISSN 1095-9203. ISSN 0036-8075.
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