Physics:Oh-My-God particle

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Short description: Ultra-high-energy cosmic ray detected in 1991


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 .[1][2][3] (As of 2024), it is the highest-energy cosmic ray ever observed.[4] Its energy was estimated as (3.2±0.9)×1020 eV (320 exa-eV). The particle's energy was unexpected and called into question prevailing theories about the origin and propagation of cosmic rays.

Speed

It is not known what kind of particle it was, but most cosmic rays are protons. If [math]\displaystyle{ m_\mathrm{p} }[/math] is the rest mass of the particle and [math]\displaystyle{ E_\mathrm{K} }[/math] is its kinetic energy (energy above the rest mass energy), then its speed was [math]\displaystyle{ \sqrt{1-[m_\mathrm{p}c^2/(E_\mathrm{K}+m_\mathrm{p}c^2)]^2} }[/math] times the speed of light. Assuming it was a proton, for which [math]\displaystyle{ m_\mathrm{p}c^2 }[/math] 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.

Collision energy

The energy of the 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 was available for its interaction with a nucleus in the Earth's atmosphere, with most of the energy remaining in the form of kinetic energy of the center of mass of the products of the interaction. If [math]\displaystyle{ m_\mathrm{t} }[/math] is the mass of the "target" nucleus, the energy available for such a collision is[5]

[math]\displaystyle{ \sqrt{ 2E_\mathrm{K}m_\mathrm{t}c^2+(m_\mathrm{p}+m_\mathrm{t})^2c^4 }-(m_\mathrm{p}+m_\mathrm{t})c^2 }[/math]

which for large [math]\displaystyle{ E_\mathrm{K} }[/math] is approximately

[math]\displaystyle{ \sqrt{ 2E_\mathrm{K}m_\mathrm{t}c^2}. }[/math]

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.[6][7] In the center-of-mass frame of reference (which moved at almost the speed of light in our frame of reference), the products of the collision would therefore have had around 2900 TeV of energy, enough to transform the nucleus into many particles, moving apart at almost the speed of light even in this center-of-mass frame of reference. As with other cosmic rays, this generated a cascade of relativistic particles as the particles interacted with other nuclei.

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 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 energy released by this extremely small particle is roughly comparable to dropping a 1 kg mass from a medium-sized building on Earth.[vague]

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). Coordinates: Sky map 5h 40m 48s, +48° 0′ 0″ 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]

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.[citation needed]

Later similar events

Since the first observation, hundreds of similar events (energy 5.7×1019 eV or greater) have been recorded, confirming the phenomenon.[9][10] 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][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. It had an energy exceeding 240 exa-electron volts (2.4×1020 eV). This particle appears to have emerged from the Local Void, an empty area of space bordering the Milky Way galaxy.[12] 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.[13]

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. et al. (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. doi:10.1086/175344. Bibcode: 1995ApJ...441..144B. 
  2. ↑ "The Fly's Eye (1981-1993) – The highest energy particle ever recorded". http://www.cosmic-ray.org/reading/flyseye.html#SEC10. 
  3. ↑ 3.0 3.1 Wolchover, Natalie (2015-05-14). "The particle that broke a cosmic speed limit". Quanta Magazine. ISSN 2640-2661. https://www.quantamagazine.org/the-particle-that-broke-a-cosmic-speed-limit-20150514/. Retrieved August 27, 2023. 
  4. ↑ Jonathan O’Callaghan (May 30, 2023). "We are finally closing in on the cosmic origins of the 'OMG particle'". New Scientist. https://www.newscientist.com/article/mg25834413-100-we-are-finally-closing-in-on-the-cosmic-origins-of-the-omg-particle/. Retrieved June 8, 2023. 
  5. ↑ Lebedev, V.; Shiltsev, V. (29 May 2014). Accelerator Physics at the Tevatron Collider. Springer. p. 1. ISBN 9781493908851. https://books.google.com/books?id=JW0gBAAAQBAJ&pg=PA1. Retrieved 3 June 2019. 
  6. ↑ Jowett, John (November 2015). "Lead-ion collisions: The LHC achieves a new energy record". https://cds.cern.ch/journal/CERNBulletin/2015/49/News%20Articles/2105084?ln=en. 
  7. ↑ Nerlich, Steve (13 June 2011). "Oh-My-God particles". https://phys.org/news/2011-06-oh-my-god-particles.html. 
  8. ↑ Aharonian, F. (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". Astronomy & Astrophysics 349: 11–28. Bibcode: 1999A&A...349...11A. https://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1999A%26A...349...11A&defaultprint=YES&filetype=.pdf. Retrieved June 19, 2023. 
  9. ↑ Abdul Halim, A.; Abreu, P.; Aglietta, M.; Allekotte, I.; Allison, P.; Almeida Cheminant, K.; Almela, A.; Alvarez-Muñiz, J. et al. (2023-02-01). "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. Bibcode: 2023ApJS..264...50A. 
  10. ↑ 10.0 10.1 Abbasi, R. U.; Abe, M.; Abu-Zayyad, T.; Allen, M.; Anderson, R. et al. (2014-07-14). "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. doi:10.1088/2041-8205/790/2/L21. ISSN 0004-637X. Bibcode: 2014ApJ...790L..21A. 
  11. ↑ Cho, Adrian (2014-07-08). "Physicists spot potential source of 'Oh-My-God' particles". Science. doi:10.1126/article.22871. ISSN 0036-8075. https://www.science.org/content/article/physicists-spot-potential-source-oh-my-god-particles. Retrieved June 30, 2022. 
  12. ↑ "'What the heck is going on?' Extremely high-energy particle detected falling to Earth.". The Guardian. 2023-11-24. https://www.theguardian.com/science/2023/nov/24/amaterasu-extremely-high-energy-particle-detected-falling-to-earth. Retrieved November 24, 2023. 
  13. ↑ "Second OMG cosmic ray particle breaks physics again". Cosmosmagazine.com. 2023-11-24. https://cosmosmagazine.com/space/astrophysics/second-largest-cosmic-ray-particle/#:~:text=The%20ultra%20high-energy%20cosmic%20ray%20was%20named%20%E2%80%9CAmaterasu%2C%E2%80%9D,in%20a%20paper%20published%20in%20the%20journal%20Science.. Retrieved November 24, 2023. 



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