Scientists Solve Mystery of Ultra-High Energy Amaterasu Particle
New research suggests the most powerful cosmic rays may be ultraheavy atomic nuclei that retain energy better while traveling through space than previously thought.
The mysterious Amaterasu particle, one of the most energetic cosmic rays ever detected, may finally have an explanation. New research published in Physical Review Letters suggests that some of the most extreme cosmic rays could be ultraheavy atomic nuclei, heavier than iron, which are better able to retain their energy during their journey through intergalactic space.
The Amaterasu particle, detected by the Telescope Array in Utah in 2021 and named for the Japanese sun goddess, carried an estimated energy of about 240 exa-electron volts. This makes it roughly 10 million times more energetic than particles produced in the Large Hadron Collider and gives it approximately the kinetic energy of a fast-moving tennis ball. The particle has puzzled scientists because its estimated arrival direction traces back to a cosmic void with no obvious source capable of producing such extreme energies.
Researchers led by Penn State's Kohta Murase propose that these ultrahigh-energy cosmic rays may be atomic nuclei heavier than iron rather than protons or lighter elements. According to their calculations, these ultraheavy nuclei lose energy more slowly than lighter particles while crossing intergalactic space, allowing them to survive the journey to Earth while maintaining extreme energy levels. This could explain how such powerful particles can reach Earth from distant cosmic sources.
The team's work, conducted with collaborators at institutions in Japan, Virginia Tech, and other universities, addresses one of astrophysics' most enduring mysteries. Ultrahigh-energy cosmic rays can only be accelerated by the most powerful sources in the universe, yet the origins of these particles have remained unclear for more than 60 years since the first example was reported. The Amaterasu particle and similar detections represent energies that exceed 100 exa-electron volts, placing them in an extremely rare category.
The research provides new insights into the types of cosmic objects powerful enough to launch such particles. By understanding that ultraheavy nuclei may be responsible for the most extreme cosmic ray events, scientists can better identify potential sources and understand the mechanisms behind these extraordinary accelerations. The work opens new avenues for studying the most violent processes in the universe and may help resolve the long-standing puzzle of cosmic ray origins.
