Astronomers Shocked by Mysterious Ultra-High-Energy Cosmic Ray – “What the Heck Is Going On?”

by Liam O'Connor
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Cosmic Rays

Astronomers Stunned by Enigmatic Ultra-High-Energy Cosmic Ray – Puzzling Phenomenon Challenges Scientific Understanding

Astrophysicists at the University of Utah and the Telescope Array have made a groundbreaking revelation by detecting cosmic rays with energy levels surpassing theoretical limits, thereby posing a profound challenge to existing particle physics knowledge. These remarkable findings, featuring the enigmatic Oh-My-God and Amaterasu particles, have given rise to significant questions about uncharted cosmic phenomena and have become the focal point of ongoing scientific inquiry.

The Amaterasu particle, recently christened as such, has emerged as the second most powerful cosmic ray, deepening the conundrum surrounding the origin, transmission, and particle physics governing these scarce ultra-high-energy cosmic rays.

In 1991, the University of Utah’s Fly’s Eye experiment detected the highest-energy cosmic ray ever recorded, subsequently named the Oh-My-God particle. This cosmic ray’s energy levels left astrophysicists astounded. Within our galaxy, no known source possessed the capability to produce such energy, and the particle exhibited more energy than theoretically deemed possible for cosmic rays traversing vast distances from distant galaxies. In simple terms, the existence of this particle defied conventional wisdom.

Since then, the Telescope Array has documented over 30 ultra-high-energy cosmic rays, yet none have approached the energy levels of the Oh-My-God particle. None of these observations have elucidated their source or how they manage to journey to Earth.

On May 27, 2021, the Telescope Array experiment identified the second-highest extreme-energy cosmic ray, boasting an energy level of 2.4 x 10^20 electronvolts—equivalent to the force of dropping a brick on one’s toe from waist height. Led by the University of Utah and the University of Tokyo, the Telescope Array comprises 507 surface detector stations arranged in a square grid, spanning an extensive 700 square kilometers (approximately 270 square miles) in the West Desert region near Delta, Utah. The event triggered 23 detectors in the northwest region of the Telescope Array, spanning an area of 48 square kilometers (18.5 square miles). Its apparent trajectory led it from the Local Void, an empty expanse of space bordering the Milky Way galaxy.

“The particles possess such immense energy that they should remain unaffected by galactic and extragalactic magnetic fields. One should theoretically be able to pinpoint their celestial origins,” remarked John Matthews, co-spokesperson for the Telescope Array and co-author of the study. “However, in the case of both the Oh-My-God particle and this new particle, tracing their trajectory back to the source yields nothing of sufficient energy to have generated them. This constitutes the mystery at hand—what precisely is transpiring?”

In their observation, detailed in the November 24, 2023, issue of the journal Science, an international consortium of researchers meticulously scrutinized the ultra-high-energy cosmic ray, assessed its characteristics, and arrived at the intriguing possibility that these rare phenomena might adhere to particle physics principles hitherto unknown to science. The researchers bestowed the moniker “Amaterasu particle” upon it, inspired by the sun goddess of Japanese mythology. The identification of both the Oh-My-God and Amaterasu particles through distinct observation techniques affirms the authenticity of these exceedingly rare, ultra-high-energy events.

“These events appear to originate from entirely disparate regions in the cosmos. There is no singular enigmatic source,” remarked John Belz, professor at the University of Utah and co-author of the study. “Speculations range from structural defects in spacetime to collisions of cosmic strings. I am, however, offering unconventional ideas proposed in light of the absence of a conventional explanation.”

Cosmic rays, in essence, represent echoes of cataclysmic celestial occurrences that have stripped matter down to its subatomic constituents, propelling it through the cosmos at nearly the speed of light. These cosmic rays encompass charged particles, spanning a spectrum of energies, including positively charged protons, negatively charged electrons, and even entire atomic nuclei. They traverse space continually and intermittently impact Earth.

Upon entering Earth’s upper atmosphere, cosmic rays engage with oxygen and nitrogen gas nuclei, resulting in the creation of numerous secondary particles. These secondary particles travel short distances within the atmosphere and initiate a chain reaction, generating a cascade of billions of secondary particles that scatter upon reaching the Earth’s surface. The footprint of this secondary shower is extensive, necessitating the deployment of detectors covering an area as vast as that of the Telescope Array. These surface detectors employ a suite of instruments to provide researchers with data about each cosmic ray: the signal’s timing reveals its trajectory, while the quantity of charged particles striking each detector discloses the primary particle’s energy.

Due to their electrical charge, cosmic particles’ trajectories resemble the erratic path of a pinball in a machine, as they zigzag while encountering electromagnetic fields within the cosmic microwave background. Tracking the trajectory of most cosmic rays, particularly those on the lower to middle spectrum of energy, is a daunting task. Even high-energy cosmic rays remain affected by the microwave background. Only the most colossal celestial events possess the capability to generate cosmic rays of Oh-My-God and Amaterasu magnitude.

“Phenomena commonly perceived as highly energetic, such as supernovae, fall woefully short in terms of energy levels for this purpose. To confine and accelerate particles at these energy levels, one requires an immense energy source and extraordinarily potent magnetic fields,” Matthews explained.

Ultra-high-energy cosmic rays must exceed the energy threshold of 5 x 10^19 electronvolts, equating a single subatomic particle’s kinetic energy to that of a professional baseball pitcher’s fastball, far surpassing the energy achievable by any human-made particle accelerator. Astrophysicists have computed this theoretical threshold, known as the Greisen–Zatsepin–Kuzmin (GZK) cutoff, as the maximum energy a proton can retain during extended journeys before the effects of interactions with microwave background radiation siphon away its energy. Known candidate sources, such as active galactic nuclei or black holes featuring accretion disks emitting particle jets, tend to lie more than 160 million light years distant from Earth. The new particle’s energy of 2.4 x 10^20 electronvolts and the Oh-My-God particle’s 3.2 x 10^20 electronvolts conspicuously exceed this cutoff.

Researchers also scrutinize the composition of cosmic rays for hints regarding their origins. Heavier particles, such as iron nuclei, possess greater mass and charge, rendering them more susceptible to deflection in magnetic fields compared to lighter particles composed of protons from hydrogen atoms. The new particle is likely a proton. Particle physics principles dictate that a cosmic ray boasting energy surpassing the GZK cutoff should remain impervious to distortion by the microwave background, yet the reverse trajectory suggests an empty expanse of space.

“It is conceivable that magnetic fields possess greater strength than previously thought, although this contradicts other observations indicating their inadequacy to induce significant curvature at these electronvolt energy levels,” Belz noted. “The mystery persists.”

The ongoing expansion of the Telescope Array holds promise for unraveling the enigma of ultra-high-energy cosmic rays. Situated at an elevation of approximately 1,200 meters (4,000 feet), the Telescope Array occupies an optimal position, allowing secondary particles to develop to their fullest extent without undergoing decay. The location in Utah’s West Desert offers advantageous atmospheric conditions: the ar

Frequently Asked Questions (FAQs) about Cosmic Rays

What are ultra-high-energy cosmic rays, and why are they significant?

Ultra-high-energy cosmic rays are subatomic particles with exceptionally high energy levels that originate from space and impact Earth. They are of great significance because their energy levels challenge our understanding of particle physics and the limits of energy in the universe.

What is the Oh-My-God particle, and why was its discovery significant?

The Oh-My-God particle is the highest-energy cosmic ray ever observed, with energy levels that should not be possible based on our current understanding of cosmic ray origins. Its discovery was significant because it raised questions about the sources of such extreme energy in the universe.

What is the Amaterasu particle, and why is it important?

The Amaterasu particle is another ultra-high-energy cosmic ray that was recently discovered. It is named after a sun goddess in Japanese mythology. Its importance lies in the fact that it deepens the mystery surrounding the origin of these high-energy cosmic rays and suggests the existence of unknown particle physics principles.

How do scientists detect and study ultra-high-energy cosmic rays?

Scientists use detectors, such as those in the Telescope Array, to observe the arrival of these cosmic rays on Earth’s surface. These detectors provide data on the energy, trajectory, and composition of the cosmic rays, which is crucial for understanding their origins and properties.

What is the Greisen-Zatsepin-Kuzmin (GZK) cutoff, and why is it relevant to ultra-high-energy cosmic rays?

The GZK cutoff is a theoretical limit on the energy of cosmic rays due to interactions with microwave background radiation during their long journeys through space. Ultra-high-energy cosmic rays that exceed this cutoff challenge our understanding because they should not be able to retain such high energy levels over cosmic distances.

What are the possible explanations for the origin of ultra-high-energy cosmic rays?

The origin of these cosmic rays remains a mystery. Speculations include defects in spacetime, collisions of cosmic strings, or the existence of as-yet-undiscovered sources of immense energy in the universe. Scientists are actively researching to uncover the truth.

How does the Telescope Array contribute to the study of ultra-high-energy cosmic rays?

The Telescope Array, with its extensive array of detectors, is uniquely positioned to observe and collect data on these cosmic rays. Its expansion aims to capture more events and shed light on the sources and properties of ultra-high-energy cosmic rays.

More about Cosmic Rays

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