The Oh-My-God particle was an
ultra-high-energy cosmic ray
In astroparticle physics, an ultra-high-energy cosmic ray (UHECR) is a cosmic ray with an energy greater than 1 EeV (1018 electronvolts, approximately 0.16 joules), far beyond both the rest mass and energies typical of other cosmic ray partic ...
detected on 15 October 1991 by the
Fly's Eye
The High Resolution Fly's Eye or HiRes detector was an ultra-high-energy cosmic ray observatory that operated in the western Utah desert from May 1997 until April 2006. HiRes used the atmospheric fluorescence technique that was pioneered ...
camera in
Dugway Proving Ground
Dugway Proving Ground (DPG) is a U.S. Army facility established in 1942 to test biological and chemical weapons, located about southwest of Salt Lake City, Utah, United States, and south of the Utah Test and Training Range.
Location
Dugway P ...
,
Utah
Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...
, U.S. It is the highest-energy
cosmic ray
Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...
ever observed.
[
This particle's energy was unexpected and called into question theories of that era about the origin and propagation of cosmic rays.
]
Comparisons
The ''Oh-My-God particle''s energy was estimated as , or . Although this amount is phenomenally large – far outstripping the highest energy that humans 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 (100 quintillion
Two naming scales for large numbers have been used in English and other European languages since the early modern era: the long and short scales. Most English variants use the short scale today, but the long scale remains dominant in many non-Eng ...
) times the photon energy
Photon energy is the energy carried by a single photon. The amount of energy is directly proportional to the photon's electromagnetic frequency and thus, equivalently, is inversely proportional to the wavelength. The higher the photon's frequency, ...
of visible light, equivalent to a baseball
Baseball is a bat-and-ball sport played between two teams of nine players each, taking turns batting and fielding. The game occurs over the course of several plays, with each play generally beginning when a player on the fielding tea ...
travelling at about . Its energy was 20 million times greater than the highest energy measured in electromagnetic radiation
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic field, electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, inf ...
emitted by an extragalactic object: The blazar
A blazar is an active galactic nucleus (AGN) with a relativistic jet (a jet composed of ionized matter traveling at nearly the speed of light) directed very nearly towards an observer. Relativistic beaming of electromagnetic radiation from the ...
Markarian 501
Markarian 501 (or Mrk 501) is a galaxy with a spectrum extending to the highest energy gamma rays. It is a blazar or BL Lac object, which is an active galactic nucleus with a jet that is shooting towards the Earth.
In the very-high-energy gamma r ...
.
Comparison to a proton
Assuming it was a proton, this particle traveled at of the speed of light
The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit ...
, its Lorentz factor
The Lorentz factor or Lorentz term is a quantity expressing how much the measurements of time, length, and other physical properties change for an object while that object is moving. The expression appears in several equations in special relativit ...
was and its rapidity
In relativity, rapidity is commonly used as a measure for relativistic velocity. Mathematically, rapidity can be defined as the hyperbolic angle that differentiates two frames of reference in relative motion, each frame being associated with di ...
was . At this speed, if a photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always ...
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
In physics, the special theory of relativity, or special relativity for short, is a scientific theory regarding the relationship between space and time. In Albert Einstein's original treatment, the theory is based on two postulates:
# The laws o ...
, 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
A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams.
Large accelerators are used for fundamental research in particle ...
. However, only a small fraction of this energy would be available
In reliability engineering, the term availability has the following meanings:
* The degree to which a system, subsystem or equipment is in a specified operable and committable state at the start of a mission, when the mission is called for at a ...
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 where is the particle's energy and is the mass-energy of the assumed proton. For the Oh-My-God particle, this gives , which is roughly 60 times higher than the highest collision energy of the Large Hadron Collider
The Large Hadron Collider (LHC) is the world's largest and highest-energy particle collider. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaboration with over 10,000 scientists and hundred ...
(as of 2015).
High, 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 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 ( times the current age of the universe
In physical cosmology, the age of the universe is the time elapsed since the Big Bang. Astronomers have derived two different measurements of the age of the universe:
a measurement based on direct observations of an early state of the universe, ...
) for a photon to overtake a Planck energy proton with a 1 cm lead.
Later similar events
Since the first observation, at least seven similar events (energy or greater) have been recorded, confirming the phenomenon. These ultra-high-energy cosmic ray particles are very rare; the energy of most cosmic ray particles is between eV and eV.
More recent studies using the Telescope Array Project
The Telescope Array project is an international collaboration involving research and educational institutions in Japan, The United States, Russia, South Korea, and Belgium. The experiment is designed to observe air showers induced by ultra-high- ...
have suggested a source of the particles within a 20 degree radius "warm spot" in the direction of the constellation Ursa Major
Ursa Major (; also known as the Great Bear) is a constellation in the northern sky, whose associated mythology likely dates back into prehistory. Its Latin name means "greater (or larger) bear," referring to and contrasting it with nearby Ursa ...
.
See also
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References
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Cosmic rays
1991 in science
1991 in Utah
Individual physical objects