Mysterious Ultra-High-Energy Cosmic Ray Recently Detected Could Be the Most Powerful Yet in 30 Years

Scientists have identified the most powerful cosmic ray in over 30 years, originating from space, yet its source remains unknown. This enigmatic particle boasted an estimated 240 exa-electron volts (EeV), comparable to the record-setting "Oh My God particle" discovered in 1991.

A cosmic ray is a high-energy subatomic particle, often a proton, traversing space at near-light speed. These ultra-high-energy cosmic rays surpass human-made particle accelerators by a factor of one million, with those exceeding 100 EeV rarely observed on Earth.

The Record-Breaking 'Oh My God Particle'

On the night of October 15, 1991, the "Oh My God particle" streaked across the Utah sky, representing a cosmic ray with an astounding 320 exa-electron volts (EeV) of energy, far surpassing particles generated in human-built accelerators.

Mengzhi "Steven" Luo and astrophysicist David Kieda operated the Fly's Eye detector, a straightforward yet efficient system of mirrors that captured the faint glow of the remarkable particle.

Despite surpassing the GZK cutoff in energy, indicating a recent and nearby origin within the local supercluster of galaxies, there was no observable astrophysical accelerator of the required magnitude in the direction from which it originated.

The discovery prompted scientists to build more sophisticated detectors, leading to the recording of hundreds of thousands of "ultra-high-energy cosmic rays." These particles, surpassing the GZK speed limit, held the potential to offer insights into physics at unprecedented scales and illuminate the workings of astrophysical phenomena.

However, the subsequent data generated confusion, challenging existing theories. Only recently, with the identification of a cosmic ray hotspot, the detection of related high-energy cosmic particles, and enhanced understanding of physics at familiar energy levels, researchers began making strides in comprehending ultrahigh-energy cosmic rays.

Amaterasu: Most Powerful Cosmic Ray in Three Decades

On May 21, 2021, scientists operating the Telescope Array project in Utah detected an extraordinary cosmic ray, marking the most powerful since the renowned "Oh My God particle" identified in 1991.

This newly discovered particle, named "Amaterasu" after the Shinto sun goddess, exhibited a staggering energy level of 244 exa-electron volts (EeV). The OMG particle, with its record-setting energy of 320 EeV, remains the most potent cosmic ray ever recorded, moving at speeds exceeding 99.9% of the speed of light.

Detailed in an upcoming study in Science by researchers from Osaka Metropolitan University (OMU), the Amaterasu finding perplexed lead author Toshihiro Fujii, who expressed surprise at the unprecedented energy level not witnessed in the past three decades.

The particle's origin poses a puzzle as its trajectory leads back to a cosmic void lacking galaxies or cosmic structures. Although potential sources such as supernova explosions, black hole mergers, and pulsars have been suggested, the researchers contemplate the possibility of novel physical origins beyond the established Standard Model of physics.

The quest for understanding ultra-high-energy (UHE) cosmic rays continues, with researchers hoping that advancements in next-generation observatories will unravel the mysteries surrounding these powerful particles, shedding light on both the newly discovered Amaterasu and the elusive OMG particle detected over 30 years ago.

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