Telescope Array detects second-highest-energy cosmic ray ever

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 vitality shocked astrophysicists. Nothing in our galaxy had the facility to provide it, and the particle had extra vitality than was theoretically doable 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 vitality. No observations have but revealed their origin or how they’re able to journey to Earth.

On Could 27, 2021, the Telescope Array experiment detected the second-highest extreme-energy cosmic ray. At 2.4 x 10²⁰eV, the vitality of this single subatomic particle is equal to dropping a brick in your toe from waist peak. Led by the College of Utah (the U) and the College of Tokyo, the experiment used the Telescope Array, which 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 path seemed to be from the Native Void, an empty space of space bordering the Milky Way galaxy.

“The particles are so excessive vitality, they should not be affected by galactic and extra-galactic magnetic fields. You need to be capable of 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 examine. “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 vitality sufficient to have produced it. That is the thriller of this—what the heck is happening?”

Of their remark published within the journal Science, a world collaboration of researchers describe the ultra-high-energy cosmic ray, consider its traits, and conclude that the uncommon phenomena would possibly comply with particle physics unknown to science.

The researchers named it the Amaterasu particle after the sun goddess in Japanese mythology. The Oh-My-God and the Amaterasu particles had been detected utilizing completely different remark strategies, confirming that whereas uncommon, these ultra-high vitality occasions are actual.

“These occasions seem to be they’re coming from utterly completely different locations within the sky. It isn’t like there’s one mysterious supply,” mentioned John Belz, professor on the U and co-author of the examine. “It might be defects within the construction of spacetime, colliding cosmic strings. I imply, I am simply spit-balling loopy concepts that persons are arising with as a result of there’s not a standard rationalization.”

Pure particle accelerators

Cosmic rays are echoes of violent celestial occasions which have stripped matter to its subatomic buildings and hurled it by universe at almost the pace of sunshine. Basically cosmic rays are charged particles with a variety of energies consisting of constructive protons, detrimental electrons, or complete atomic nuclei that journey by space and rain down onto Earth almost continually.

Cosmic rays hit Earth’s higher ambiance and blasts aside the nucleus of oxygen and nitrogen fuel, producing many secondary particles. These journey a brief distance within the ambiance and repeat the method, constructing a bathe of billions of secondary particles that scatter to the floor. The footprint of this secondary bathe is huge and requires that detectors cowl an space as giant because the Telescope Array. The floor detectors make the most of a collection of instrumentation that offers 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 vitality.

As a result of particles have a cost, their flight path resembles a ball in a pinball machine as they zigzag in opposition to the electromagnetic fields by the cosmic microwave background. It is almost not possible to hint the trajectory of most cosmic rays, which lie on the low- to middle-end of the vitality spectrum. Even high-energy cosmic rays are distorted by the microwave background. Particles with Oh-My-God and Amaterasu vitality blast by intergalactic space comparatively unbent. Solely essentially the most highly effective of celestial occasions can produce them.

“Issues that folks consider as energetic, like supernova, are nowhere close to energetic sufficient for this. You want enormous quantities of vitality, 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. Because of this a single subatomic particle carries the identical kinetic vitality as a significant league pitcher’s fastball and has tens of thousands and thousands of occasions extra vitality than any human-made particle accelerator can obtain.

Astrophysicists calculated this theoretical restrict, referred to as the Greisen–Zatsepin–Kuzmin (GZK) cutoff, as the utmost vitality a proton can maintain touring over lengthy distances earlier than the impact of interactions of the microwave background radiation takes their vitality.

Identified supply candidates, akin to active galactic nuclei or black holes with accretion disks emitting particle jets, are typically greater than 160 million mild 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 vitality past the GZK cutoff is simply too highly effective for the microwave background to distort its path, however back-tracing its trajectory factors in the direction of empty space.

“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 10²⁰ 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 candy spot that enables secondary particles most growth, however earlier than they begin to decay. Its location in Utah’s West Desert gives splendid atmospheric situations in two methods: the dry air is essential as a result of humidity will take in the ultraviolet mild needed for detection; and the area’s darkish skies are important, as mild 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 growth that that they hope will assist crack the case. As soon as accomplished, 500 new scintillator detectors will increase the Telescope Array will pattern cosmic ray-induced particle showers throughout 2,900 km² (1,100 mi² ), an space almost the scale of Rhode Island. The bigger footprint will hopefully seize extra occasions that may make clear what is going on on.