An illustration depicting a cosmic ray impacting the Telescope Array experiment’s detectors in 2021. (Image credit: Osaka Metropolitan University/L-INSIGHT, Kyoto University/Ryuunosuke Takeshige)
Researchers are currently focused on unraveling the source of an exceptionally powerful particle detected arriving at Earth from outer space. Dubbed the Amaterasu particle, after the revered Japanese sun goddess, its initial detection occurred in 2021. This energetic particle possesses approximately 40 million times the energy of particles generated by the Large Hadron Collider (LHC), the world’s foremost particle accelerator.
Investigating Ultra-High-Energy Cosmic Rays
Amaterasu represents an example of a cosmic ray – highly energetic, charged particles traversing the cosmos at velocities approaching the speed of light. It currently ranks as the second most energetic cosmic ray ever recorded, trailing only the “Oh-My-God” particle, which was observed in 1991. The extreme rarity of these high-energy events motivates scientists to pinpoint their origins, which are theorized to involve the remnants of supernova explosions and the active cores of galaxies hosting supermassive black holes.
New Insights into Amaterasu’s Potential Origin
A recent study led by Francesca Capel and Nadine Bourriche of the Max Planck Institute for Physics challenges the prevailing assumption that Amaterasu originated within the relatively empty expanse of the Local Void. Their findings suggest a more localized source for this extraordinary particle. “Our results suggest that, rather than originating in a low-density region of space like the Local Void, the Amaterasu particle is more likely to have been produced in a nearby star-forming galaxy such as M82,” stated Bourriche.
The team employed a sophisticated, data-driven methodology to retrace the potential trajectory of Amaterasu across the universe. Utilizing a three-dimensional statistical technique known as Approximate Bayesian Computation, they modeled the particle’s journey, accounting for the influence of interstellar magnetic fields. This method functions by comparing the outcomes of detailed, physics-based simulations with actual observational data to determine the most probable source locations.
Mapping the Probable Source Locations
The analysis yielded a series of “probability maps,” all indicating potential origin points for Amaterasu situated beyond the boundaries of the Local Void. This research extends beyond simply identifying the source of this singular particle. It offers valuable clues regarding the cosmic events capable of accelerating particles to such immense energies, effectively functioning as cosmic ray “factories.”
“Exploring ultra-high-energy cosmic rays helps us to better understand how the Universe can accelerate matter to such energies, and also to identify environments where we can study the behavior of matter in such extreme conditions,” explained Capel. “Our goal is to develop advanced statistical analysis methods to exploit the available data to its full potential and gain a deeper understanding of the possible sources of these energetic particles.” The team’s findings were published on January 28 in The Astrophysical Journal.
