A Particle with Unmatched Fury Strikes Earth (Image Credits: Dailygalaxy.com)
Researchers have traced the probable source of the Amaterasu particle, the second-most energetic cosmic ray on record, to a dynamic star-forming galaxy just 12 million light-years away.[1][2]
A Particle with Unmatched Fury Strikes Earth
On May 27, 2021, detectors at the Telescope Array experiment in Utah registered an extraordinary event. A single subatomic particle plunged into Earth’s atmosphere, unleashing a shower of secondary particles across a 700-square-kilometer area. Scientists calculated its energy at 244 exa-electronvolts, equivalent to about 40 joules – roughly 40 million times the energy of protons accelerated at the Large Hadron Collider.[3][4]
This cosmic ray, named Amaterasu after the Japanese sun goddess, ranked as the second-highest-energy particle ever observed. Such ultra-high-energy cosmic rays remain exceedingly rare, arriving from the universe’s most violent corners. The detection highlighted the Telescope Array’s precision, with its surface detectors capturing timing and density data to reconstruct the event’s properties.[3]
Yet the particle’s identity stayed elusive. It could have been a proton, a light nucleus, or even a heavy iron nucleus. Regardless, its immense power defied easy explanation.
The Enigma of the Local Void Direction
Initial analysis pointed Amaterasu’s trajectory toward the Local Void, a vast, nearly empty expanse in the cosmic large-scale structure. This region lacks known galaxies or energetic phenomena capable of generating such extreme particles. The mismatch puzzled astronomers, as cosmic rays bend along paths warped by interstellar and intergalactic magnetic fields.[2][1]
Traditional backtracking assumed minimal deflections, but models incorporating galactic magnetic fields still failed to align the direction with plausible sources. Candidates like distant active galaxies fell beyond the GZK cutoff distance, where interactions with cosmic microwave background photons should degrade such energies. The void’s emptiness suggested gaps in our knowledge of particle physics or nearby accelerators.[3]
Advanced Simulations Unlock the Likely Source
A team at the Max Planck Institute for Physics reframed the mystery with cutting-edge tools. Francesca Capel, leader of the Astrophysical Messengers group, and PhD student Nadine Bourriche developed three-dimensional simulations of cosmic-ray propagation through magnetic fields. They paired these with Approximate Bayesian Computation, a statistical method that compares simulated paths against observational data to produce probability maps of origins.[5][4]
Their work, published in The Astrophysical Journal, shifted focus from the void. “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,” Bourriche stated.[1]
This data-driven approach overcame limitations of simple directional estimates, accounting for deflections and generating robust source probabilities.
M82: The Starburst Galaxy Powerhouse
Messier 82, or M82, lies 12 million light-years distant in the constellation Ursa Major. Known as the Cigar Galaxy for its elongated shape, it exemplifies a starburst galaxy – where stars form at rates hundreds of times higher than in the Milky Way. These frenzied environments host supernovae, black holes, and powerful outflows that could accelerate particles to ultra-high energies.[2]
Key features of starburst galaxies like M82 include:
- Intense star formation fueling shocks and turbulence.
- Superwinds expelling gas at high speeds.
- Compact regions amplifying magnetic fields for particle acceleration.
- Proximity allowing survival past the GZK limit.
Such galaxies emerge as prime suspects for ultra-high-energy cosmic rays, bridging the gap between theory and sparse detections.
Capel emphasized the broader value: “Exploring ultra-high-energy cosmic rays helps us to better understand how the Universe can accelerate matter to such energies.”[1]
Key Takeaways
- Amaterasu’s 244 EeV energy dwarfs human-made accelerators by 40 million times.
- New simulations favor M82 over the empty Local Void as the source.
- Advanced stats pave the way for pinpointing other cosmic ray origins.
This discovery advances our grasp of cosmic accelerators and equips future observatories to hunt high-energy messengers. What sources do you suspect for the next big cosmic ray detection? Share your thoughts in the comments.
