View source for Oh-My-God particle

{{Short description|Ultra-high-energy cosmic ray detected in 1991}}
{{Distinguish|text=the "God Particle", or [[Higgs boson]]}}
{{Use American English|date=March 2021}}
{{Use mdy dates|date=March 2021}}

The '''Oh-My-God particle''' was an [[ultra-high-energy cosmic ray]] detected on 15&nbsp;October 1991 by the [[Fly's Eye]] camera in [[Dugway Proving Ground]], [[Utah]], [[United States]].<ref>{{cite journal |last1=Bird |first1=D. J. |last2=Corbato |first2=S. C. |last3=Dai |first3=H. Y. |last4=Elbert |first4=J. W. |last5=Green |first5=K. D. |last6=Huang |first6=M. A. |last7=Kieda |first7=D. B. |last8=Ko |first8=S. |last9=Larsen |first9=C. G. |last10=Loh |first10=E. C. |last11=Luo |first11=M. Z. |last12=Salamon |first12=M. H. |last13=Smith |first13=J. D. |last14=Sokolsky |first14=P. |last15=Sommers |first15=P. |date=March 1995 |title=Detection of a cosmic ray with measured energy well beyond the expected spectral cutoff due to cosmic microwave radiation |journal=[[The Astrophysical Journal]] |volume=441 |pages=144 |arxiv=astro-ph/9410067 |bibcode=1995ApJ...441..144B |doi=10.1086/175344 |s2cid=119092012 |doi-access=free |last16=Tang |first16=J. K. K. |last17=Thomas |first17=S. B.}}</ref><ref>{{cite web |last=<!-- no author attribution --> |date=<!-- not specified --> |title=HiRes – The High Resolution Fly's Eye Ultra High Energy Cosmic Ray Observatory |url=http://www.cosmic-ray.org/reading/flyseye.html#SEC10 |url-status=live |archive-url=https://web.archive.org/web/20090815102123/http://www.cosmic-ray.org/reading/flyseye.html#SEC10 |archive-date=August 15, 2009 |access-date=February 6, 2024 |website=H i R e s / High Resolution Fly's Eye |publisher=[[University of Utah]] |at=The highest energy particle ever recorded}}</ref><ref name=q/> {{Asof|2023}}, it is the highest-energy [[cosmic ray]] ever observed.<ref>{{cite journal |last1=O’Callaghan |first1=Jonathan |date=May 30, 2023 |title=We are finally closing in on the cosmic origins of the 'OMG particle' |url=https://www.newscientist.com/article/mg25834413-100-we-are-finally-closing-in-on-the-cosmic-origins-of-the-omg-particle/ |url-status=live |journal=[[New Scientist]] |url-access=limited |archive-url=https://web.archive.org/web/20230609005718/https://www.newscientist.com/article/mg25834413-100-we-are-finally-closing-in-on-the-cosmic-origins-of-the-omg-particle/ |archive-date=June 9, 2023 |access-date=June 8, 2023}}</ref> Its energy was estimated as {{val|3.2|0.9|e=20|ul=eV}} (320 [[metric prefix|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 ray]]s are protons. If <math>m_\mathrm{p}</math> is the [[rest mass]] of the particle and <math>E_\mathrm{K}</math> is its [[kinetic energy]] (energy above the [[rest mass energy]]), then its speed was very close to <math display=inline>\sqrt{1-[m_\mathrm{p}c^2/(E_\mathrm{K}+m_\mathrm{p}c^2)]^2}</math> times the [[speed of light]]. Since <math display=inline>E_\mathrm{K} \gg m_\mathrm{p}c^2</math>, this ratio can be simplified to <math display=inline>1-\frac{1}{2}[m_\mathrm{p}c^2/E_\mathrm{K}]^2</math>. Assuming it was a proton, for which <math>m_\mathrm{p}c^2</math> is 938&nbsp;MeV, this means it was traveling at {{val|0.9999999999999999999999957}} times the speed of light, its [[Lorentz factor]] was {{val|3.2|e=11}} and its [[rapidity]] was {{val|27.1}}. This is 1.3 [[femtometers]] per second less than the speed of light, so if a [[photon]] were traveling alongside the proton, it would take over 245,000&nbsp;years for the photon to gain a 1&nbsp;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&nbsp;billion light years, it would take approximately 1.71&nbsp;days in the [[reference frame]] of the proton to travel that distance.

==Collision energy==
The energy of the particle was some 40&nbsp;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 energy (particle collision)|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>m_\mathrm{t}</math> is the mass of the "target" nucleus, the energy available for such a collision is<ref>{{cite book |url=https://books.google.com/books?id=JW0gBAAAQBAJ&pg=PA1 |title=Accelerator Physics at the Tevatron Collider |vauthors=Holmes S, Moore R, Peoples J, Shiltsev V |date=29 May 2014 |publisher=Springer |isbn=9781493908851 |veditors=Lebedev V, [[Vladimir Shiltsev|Shiltsev V]] |series=Particle Acceleration and Detection |page=1 |chapter=Chapter 1. Introduction |doi=10.1007/978-1-4939-0885-1 |access-date=6 February 2024 |via=Google Books}}</ref>

<math display=block>\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>E_\mathrm{K}</math> is approximately

<math display=block>\sqrt{ 2E_\mathrm{K}m_\mathrm{t}c^2}.</math>

For the Oh-My-God particle hitting a [[nitrogen]] nucleus, this gives 2900&nbsp;TeV, which is roughly 200&nbsp;times higher than the highest collision energy of the [[Large Hadron Collider]], in which two high-energy particles going opposite directions collide.<ref>{{cite news |author=Jowett, John |date=November 2015 |title=Lead-ion collisions: The LHC achieves a new energy record |website=CERN Bulletin |url=https://cds.cern.ch/journal/CERNBulletin/2015/49/News%20Articles/2105084?ln=en |access-date=February 24, 2016 |archive-date=August 26, 2023 |archive-url=https://web.archive.org/web/20230826152920/https://cds.cern.ch/journal/CERNBulletin/2015/49/News%20Articles/2105084?ln=en |url-status=live }}</ref><ref>{{cite news |author=Nerlich, Steve |date=13 June 2011 |title=Oh-My-God particles |website=[[Universe Today]] |via=phys.org |url=https://phys.org/news/2011-06-oh-my-god-particles.html |access-date=June 30, 2019 |archive-date=June 30, 2019 |archive-url=https://web.archive.org/web/20190630191829/https://phys.org/news/2011-06-oh-my-god-particles.html |url-status=live }}</ref> In the center-of-mass frame of reference (which was moving, in our frame of reference, at almost the speed of light), the products of the collision would therefore have had around 2900&nbsp;TeV of energy. This would have transformed the nucleus into many particles moving apart at almost light speed in the center-of-mass frame of reference. As with other cosmic rays, the collision generated a cascade of relativistic particles as the particles interacted with other nuclei.

==Comparisons==
{{original research section|date=April 2023}}
The ''Oh-My-God particle''{{'}}s energy was estimated as {{val|3.2|0.9|e=20|ul=eV}}, or {{val|51|14|ul=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. Though a [[subatomic particle]], its energy was comparable to the [[Gravitational potential energy#Formulation|gravitational potential energy]] of a 1&nbsp;[[kilogram]] object that could fall 5&nbsp;[[meters]] off a two-story building.

The ''Oh-My-God particle'' had {{10^|20}} (100&nbsp;[[quintillion]]) times the [[photon energy]] of visible light, equivalent to a {{convert|5|oz|order=flip|adj=on|sp=us}} [[baseball (object)|baseball]] travelling at about {{convert|28|m/s|km/h mph|abbr=on}}. {{Sky|5|40|48|+|48|0|0|98000000}} Its energy was 20&nbsp;million times greater than the [[very-high-energy gamma ray|highest photon energy measured]] in [[electromagnetic radiation]] emitted by an extragalactic object, the [[blazar]] [[Markarian 501]].<ref>{{cite journal |author1=Aharonian, F. |collaboration=The HEGRA Collaboration |year=1999 |title=The time averaged TeV energy spectrum of Mkn&nbsp;501 of the extraordinary 1997 outburst as measured with the stereoscopic Cherenkov telescope system of HEGRA |journal=[[Astronomy & Astrophysics]] |volume=349 |pages=11–28 |arxiv=astro-ph/9903386v2 |bibcode=1999A&A...349...11A |s2cid=15448541 |url=https://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1999A%26A...349...11A&defaultprint=YES&filetype=.pdf |access-date=June 19, 2023 |archive-date=June 19, 2023 |archive-url=https://web.archive.org/web/20230619200950/https://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1999A%26A...349...11A&defaultprint=YES&filetype=.pdf |url-status=live }}</ref>{{update-inline|date=February 2022}}

It had a [[relativistic mass]] equivalent to around {{val|3.4|e=11}} [[dalton (unit)|daltons]], or {{val|2.4|e=10}} nitrogen nuclei.

===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&nbsp;million times ''lower'' than the [[Planck energy]] ({{val|1.2208901|e=28|u=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 {{val|1.665|e=15}} 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 {{val|3.579|e=20|u=years}} ({{val|2.59|e=10}}&nbsp;times the current [[age of the universe]]) for a photon to overtake a Planck energy proton with a 1&nbsp;cm lead.{{citation needed |date=March 2020}}

==Later similar events==
Since the first observation, hundreds of similar events (energy {{val|5.7|e=19|u=eV}} or greater) have been recorded, confirming the phenomenon.<ref>{{Cite journal |last1=Abdul Halim |first1=A. |last2=Abreu |first2=P. |last3=Aglietta |first3=M. |last4=Allekotte |first4=I. |last5=Allison |first5=P. |last6=Almeida Cheminant |first6=K. |last7=Almela |first7=A. |last8=Alvarez-Muñiz |first8=J. |last9=Ammerman Yebra |first9=J. |last10=Anastasi |first10=G. A. |last11=Anchordoqui |first11=L. |last12=Andrada |first12=B. |last13=Andringa |first13=S. |last14=Aramo |first14=C. |last15=Araújo Ferreira |first15=P. R. |date=2023-02-01 |title=A Catalog of the Highest-energy Cosmic Rays Recorded during Phase I of Operation of the Pierre Auger Observatory |journal=The Astrophysical Journal Supplement Series |volume=264 |issue=2 |pages=50 |doi=10.3847/1538-4365/aca537 |bibcode=2023ApJS..264...50A |s2cid=254070054 |issn=0067-0049 |doi-access=free |hdl=2133/25771 |hdl-access=free }}</ref><ref name="Abbasi">{{cite journal | last1 = Abbasi | first1 = R. U. | last2 = Abe | first2 = M. | last3 = Abu-Zayyad | first3 = T. | last4 = Allen | first4 = M. | last5 = Anderson | first5 = R. | last6 = Azuma | first6 = R. | last7 = Barcikowski | first7 = E. | last8 = Belz | first8 = J. W. | last9 = Bergman | first9 = D. R. | last10 = Blake | first10 = S. A. | last11 = Cady | first11 = R. | last12 = Chae | first12 = M. J. | last13 = Cheon | first13 = B. G. | last14 = Chiba | first14 = J. | last15 = Chikawa | first15 = M. | last16 = Cho | first16 = W. 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H. | last44 = Kitamura | first44 = S. | last45 = Kitamura | first45 = Y. | last46 = Kuzmin | first46 = V. | last47 = Kwon | first47 = Y. J. | last48 = Lan | first48 = J. | last49 = Lim | first49 = S. I. | last50 = Lundquist | first50 = J. P. | last51 = Machida | first51 = K. | last52 = Martens | first52 = K. | last53 = Matsuda | first53 = T. | last54 = Matsuyama | first54 = T. | last55 = Matthews | first55 = J. N. | last56 = Minamino | first56 = M. | last57 = Mukai | first57 = K. | last58 = Myers | first58 = I. | last59 = Nagasawa | first59 = K. | last60 = Nagataki | first60 = S. | last61 = Nakamura | first61 = T. | last62 = Nonaka | first62 = T. | last63 = Nozato | first63 = A. | last64 = Ogio | first64 = S. | last65 = Ogura | first65 = J. | last66 = Ohnishi | first66 = M. | last67 = Ohoka | first67 = H. | last68 = Oki | first68 = K. | last69 = Okuda | first69 = T. | last70 = Ono | first70 = M. | last71 = Oshima | first71 = A. | last72 = Ozawa | first72 = S. | last73 = Park | first73 = I. H. | last74 = Pshirkov | first74 = M. S. | last75 = Rodriguez | first75 = D. C. | last76 = Rubtsov | first76 = G. | last77 = Ryu | first77 = D. | last78 = Sagawa | first78 = H. | last79 = Sakurai | first79 = N. | last80 = Sampson | first80 = A. L. | last81 = Scott | first81 = L. M. | last82 = Shah | first82 = P. D. | last83 = Shibata | first83 = F. | last84 = Shibata | first84 = T. | last85 = Shimodaira | first85 = H. | last86 = Shin | first86 = B. K. | last87 = Smith | first87 = J. D. | last88 = Sokolsky | first88 = P. | last89 = Springer | first89 = R. W. | last90 = Stokes | first90 = B. T. | last91 = Stratton | first91 = S. R. | last92 = Stroman | first92 = T. A. | last93 = Suzawa | first93 = T. | last94 = Takamura | first94 = M. | last95 = Takeda | first95 = M. | last96 = Takeishi | first96 = R. | last97 = Taketa | first97 = A. | last98 = Takita | first98 = M. | last99 = Tameda | first99 = Y. | last100 = Tanaka | first100 = H. | last101 = Tanaka | first101 = K. | last102 = Tanaka | first102 = M. | last103 = Thomas | first103 = S. B. | last104 = Thomson | first104 = G. B. | last105 = Tinyakov | first105 = P. | last106 = Tkachev | first106 = I. | last107 = Tokuno | first107 = H. | last108 = Tomida | first108 = T. | last109 = Troitsky | first109 = S. | last110 = Tsunesada | first110 = Y. | last111 = Tsutsumi | first111 = K. | last112 = Uchihori | first112 = Y. | last113 = Udo | first113 = S. | last114 = Urban | first114 = F. | last115 = Vasiloff | first115 = G. | last116 = Wong | first116 = T. | last117 = Yamane | first117 = R. | last118 = Yamaoka | first118 = H. | last119 = Yamazaki | first119 = K. | last120 = Yang | first120 = J. | last121 = Yashiro | first121 = K. | last122 = Yoneda | first122 = Y. | last123 = Yoshida | first123 = S. | last124 = Yoshii | first124 = H. | last125 = Zollinger | first125 = R. | last126 = Zundel | first126 = Z. | display-authors = 5 |title=Indications of intermediate-scale anisotropy of cosmic rays with energy greater than 57&nbsp;EeV in the northern sky, measured with the surface detector of the Telescope Array Experiment |journal=[[The Astrophysical Journal]] |date=2014-07-14 |volume=790 |issue=2 |page=L21 |doi=10.1088/2041-8205/790/2/L21 |arxiv=1404.5890 |bibcode=2014ApJ...790L..21A|s2cid=118481211 | issn = 0004-637X | eissn = 1538-4357  }}</ref> These ultra-high-energy cosmic ray particles are very rare; the energy of most cosmic ray particles is between {{10^|7}}&nbsp;eV and {{10^|10}}&nbsp;eV.<!-- orig. 10 MeV – 10 GeV, switched to powers of 10 to compare with 5.7×10^19 at ¶ start -->

More recent studies using the [[Telescope Array Project]] have suggested a source of the particles within a 20&nbsp;degree radius "warm spot" in the direction of the constellation [[Ursa Major]].<ref name="q">{{cite journal |last1=Wolchover |first1=Natalie |author-link=Natalie Wolchover |date=May 14, 2015 |title=The particle that broke a cosmic speed limit |url=https://www.quantamagazine.org/the-particle-that-broke-a-cosmic-speed-limit-20150514/ |url-status=live |journal=[[Quanta Magazine]] |issn=2640-2661 |archive-url=https://web.archive.org/web/20230708064650/https://www.quantamagazine.org/the-particle-that-broke-a-cosmic-speed-limit-20150514/ |archive-date=July 8, 2023 |access-date=February 6, 2024 |df=dmy-all}}</ref><ref name="Abbasi" /><ref>{{cite journal |url=https://www.science.org/content/article/physicists-spot-potential-source-oh-my-god-particles |title=Physicists spot potential source of 'Oh-My-God' particles |journal=[[Science (journal)|Science]] |date=2014-07-08 |first=Adrian |last=Cho |doi=10.1126/article.22871 |doi-broken-date=November 1, 2024 |issn=0036-8075 |eissn=1095-9203 |df=dmy-all |access-date=June 30, 2022 |archive-date=April 12, 2022 |archive-url=https://web.archive.org/web/20220412155837/https://www.science.org/content/article/physicists-spot-potential-source-oh-my-god-particles |url-status=live }}</ref>

The [[Amaterasu particle]], named after the [[Amaterasu|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 ({{val|2.4|e=20}} eV).<ref>{{Cite journal |last=Conover |first=Emily |date=January 13, 2024 |title=A high-energy cosmic ray hails from the void |url=https://www.sciencenews.org/article/rare-energetic-cosmic-ray-mysterious-origins |journal=[[Science News]] |pages=5}}</ref> This particle appears to have emerged from the [[Local Void]], an empty area of space bordering the [[Milky Way]] galaxy.<ref>{{cite journal |last1=Devlin |first1=Hannah |date=2023-11-24 |title='What the heck is going on?' Extremely high-energy particle detected falling to Earth. |url=https://www.theguardian.com/science/2023/nov/24/amaterasu-extremely-high-energy-particle-detected-falling-to-earth |url-status=live |journal=[[The Guardian]] |archive-url=https://web.archive.org/web/20231124093358/https://www.theguardian.com/science/2023/nov/24/amaterasu-extremely-high-energy-particle-detected-falling-to-earth |archive-date=November 24, 2023 |access-date=February 6, 2024}}</ref> 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.<ref>{{cite journal|first1=|last1=|title=Second OMG cosmic ray particle breaks physics again|journal=[[Cosmosmagazine.com]]|url=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.|date=2023-11-24|access-date=November 24, 2023|archive-date=November 24, 2023|archive-url=https://web.archive.org/web/20231124121233/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.|url-status=live}}</ref>

==See also==
*{{annotated link|Greisen–Zatsepin–Kuzmin limit}}
*{{annotated link|HZE ion}}
*{{annotated link|Solar energetic particles}}
* [[Amaterasu particle]] (2021) – 240 Eev

==References==
{{reflist |25em}}
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[[Category:Cosmic rays]]
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