In 1991, the College of Utah Fly’s Eye experiment detected the highest-energy cosmic ray ever noticed. Later dubbed the Oh-My-God particle, the cosmic ray’s power shocked astrophysicists. Nothing in our galaxy had the facility to provide it, and the particle had extra power than was theoretically attainable for cosmic rays touring to Earth from different galaxies. Merely put, the particle shouldn’t exist.
The Telescope Array has since noticed greater than 30 ultra-high-energy cosmic rays, although none approaching the Oh-My-God-level power. No observations have but revealed their origin or how they can journey to the Earth.
On Might 27, 2021, the Telescope Array experiment detected the second-highest extreme-energy cosmic ray. At 2.4 x 1020eV, the power of this single subatomic particle is equal to dropping a brick in your toe from waist top. Led by the College of Utah (the U) and the College of Tokyo, the Telescope Array consists of 507 floor detector stations organized in a sq. grid that covers 700 km2 (~270 miles2) exterior of Delta, Utah within the state’s West Desert. The occasion triggered 23 detectors on the north-west area of the Telescope Array, splashing throughout 48 km2 (18.5 mi2). Its arrival course gave the impression to be from the Native Void, an empty space of house bordering the Milky Method galaxy.
“The particles are so excessive power, they should not be affected by galactic and extra-galactic magnetic fields. You must have the ability to level to the place they arrive from within the sky,” mentioned John Matthews, Telescope Array co-spokesperson on the U and co-author of the research. “However within the case of the Oh-My-God particle and this new particle, you hint its trajectory to its supply and there is nothing excessive power sufficient to have produced it. That is the thriller of this — what the heck is happening?”
Of their statement that revealed on Nov. 24, 2023, within the journal Science, a global collaboration of researchers describe the ultra-high-energy cosmic ray, consider its traits, and conclude that the uncommon phenomena may comply with particle physics unknown to science. The researchers named it the Amaterasu particle after the solar goddess in Japanese mythology. The Oh-My-God and the Amaterasu particles have been detected utilizing totally different statement strategies, confirming that whereas uncommon, these ultra-high power occasions are actual.
“These occasions look like they’re coming from fully totally different locations within the sky. It is not like there’s one mysterious supply,” mentioned John Belz, professor on the U and co-author of the research. “It may very well be defects within the construction of spacetime, colliding cosmic strings. I imply, I am simply spit-balling loopy concepts that individuals are arising with as a result of there’s not a traditional rationalization.”
Pure particle accelerators
Cosmic rays are echoes of violent celestial occasions which have stripped matter to its subatomic constructions and hurled it by way of universe at practically the velocity of sunshine. Primarily cosmic rays are charged particles with a variety of energies consisting of optimistic protons, destructive electrons, or whole atomic nuclei that journey by way of house and rain down onto Earth practically consistently.
Cosmic rays hit Earth’s higher environment and blasts aside the nucleus of oxygen and nitrogen gasoline, producing many secondary particles. These journey a brief distance within the environment and repeat the method, constructing a bathe of billions of secondary particles that scatter to the floor. The footprint of this secondary bathe is very large and requires that detectors cowl an space as massive because the Telescope Array. The floor detectors make the most of a collection of instrumentation that provides researchers details about every cosmic ray; the timing of the sign exhibits its trajectory and the quantity of charged particles hitting every detector reveals the first particle’s power.
As a result of particles have a cost, their flight path resembles a ball in a pinball machine as they zigzag towards the electromagnetic fields by way of the cosmic microwave background. It is practically not possible to hint the trajectory of most cosmic rays, which lie on the low- to middle-end of the power spectrum. Even high-energy cosmic rays are distorted by the microwave background. Particles with Oh-My-God and Amaterasuenergy blast by way of intergalactic house comparatively unbent. Solely probably the most highly effective of celestial occasions can produce them.
“Issues that individuals consider as energetic, like supernova, are nowhere close to energetic sufficient for this. You want large quantities of power, actually excessive magnetic fields to restrict the particle whereas it will get accelerated,” mentioned Matthews.
Extremely-high-energy cosmic rays should exceed 5 x 1019 eV. Which means that a single subatomic particle carries the identical kinetic power as a serious league pitcher’s quick ball and has tens of thousands and thousands of occasions extra power than any human-made particle accelerator can obtain. Astrophysicists calculated this theoretical restrict, generally known as the Greisen-Zatsepin-Kuzmin (GZK) cutoff, as the utmost power a proton can maintain touring over lengthy distances earlier than the impact of interactions of the microwave background radiation take their power. Identified supply candidates, corresponding to lively galactic nuclei or black holes with accretion disks emitting particle jets, are usually greater than 160 million gentle years away from Earth. The brand new particle’s 2.4 x 1020 eV and the Oh-My-God particle’s 3.2 x 1020 eV simply surpass the cutoff.
Researchers additionally analyze cosmic ray composition for clues of its origins. A heavier particle, like iron nuclei, are heavier, have extra cost and are extra prone to bending in a magnetic area than a lighter particle product of protons from a hydrogen atom. The brand new particle is probably going a proton. Particle physics dictates {that a} cosmic ray with power past the GZK cutoff is just too highly effective for the microwave background to distort its path, however again tracing its trajectory factors in direction of empty house.
“Possibly magnetic fields are stronger than we thought, however that disagrees with different observations that present they don’t seem to be robust sufficient to provide important curvature at these ten-to-the-twentieth electron volt energies,” mentioned Belz. “It is an actual thriller.”
Increasing the footprint
The Telescope Array is uniquely positioned to detect ultra-high-energy cosmic rays. It sits at about 1,200 m (4,000 ft), the elevation sweet-spot that enables secondary particles most improvement, however earlier than they begin to decay. Its location in Utah’s West Desert supplies ideally suited atmospheric situations in two methods: the dry air is essential as a result of humidity will take in the ultraviolet gentle essential for detection; and the area’s darkish skies are important, as gentle air pollution will create an excessive amount of noise and obscure the cosmic rays.
Astrophysicists are nonetheless baffled by the mysterious phenomena. The Telescope Array is in the course of an enlargement that that they hope will assist crack the case. As soon as accomplished, 500 new scintillator detectors will broaden the Telescope Array will pattern cosmic ray-induced particle showers throughout 2,900 km2 (1,100 mi2 ), an space practically the dimensions of Rhode Island. The bigger footprint will hopefully seize extra occasions that can make clear what is going on on.
