Cosmic rays, also known as astroparticles, help scientists explore the mysteries of our universe. These charged particles, primarily protons, travel almost at the speed of light. When they hit Earth, most get deflected by our planet’s magnetosphere, but a few penetrate our atmosphere and reach the ground. Studying them gives clues about the forces shaping our solar system and the Milky Way.
In May 2021, researchers from the Telescope Array Project detected an extraordinary cosmic ray dubbed the Amaterasu particle, named after a Japanese sun goddess. This particle had approximately 40 million times more energy than those smashed together in the Large Hadron Collider, making it one of the highest-energy cosmic rays ever recorded. Thanks to scientists like Francesca Capel and Nadine Bourriche from the Max Planck Institute for Physics, the search for its origin is now more defined.
When the Amaterasu particle entered our atmosphere, it registered an energy level exceeding 240 exa-electronvolts (EeV). Such high-energy particles are rare. Initially, scientists were uncertain if it was a proton, a light nucleus, or a heavier nucleus, like iron. Their research suggest it might come from the Local Void, a large area near us with few galaxies.
This poses a big puzzle. The Local Void lacks the sources needed to produce such powerful particles. To tackle this, Capel and Bourriche used advanced simulations alongside statistical methods to create three-dimensional maps showing how cosmic rays move and interact within the Milky Way. Their findings hinted that the Amaterasu particle might not be tied solely to the Local Void. Instead, it could originate from neighboring cosmic environments, like the M82 Cigar Galaxy, just 12 million light-years away. Bourriche noted, “Our results suggest that the Amaterasu particle is more likely produced in a nearby star-forming galaxy, like M82.”
Capel emphasized the significance of their research: “Exploring ultra-high-energy cosmic rays helps us understand how the Universe accelerates matter to such extreme energies. We aim to refine statistical methods to make the most of available data and deepen our insights into these energetic particles’ sources.”
Their work was published in a paper titled “Beyond the Local Void: A Data-driven Search for the Origins of the Amaterasu Particle” on January 28th in The Astrophysical Journal. As research in this field evolves, it provides a fascinating glimpse into how we understand our universe and the conditions within it.
Further Reading: MPG
