In recent scientific developments, the discovery of an exceptionally energetic cosmic ray, named “Amaterasu” after the Japanese sun goddess, is challenging our understanding of physics and the universe. Detected by Dr. Toshihiro Fujii of Osaka Metropolitan University while analyzing data from the Telescope Array Project in the U.S., this cosmic ray has an energy of 240 exa-electron-volts (EeV), making it the second-highest-energy cosmic ray ever recorded. For context, the energy of 1 eV is significantly smaller than a joule, but in the realm of subatomic particles, it is a substantial measure.
The journey of these ultra-high-energy cosmic rays (UHECRs) is a topic of great interest. It’s estimated that these particles, moving near the speed of light, travel distances of 50-100 megaparsecs, which is about 1,500-3,000 billion billion km, taking 3-10 million years to reach us. This immense journey causes them to lose energy due to interactions with the cosmic microwave background (CMB). Interestingly, the point of origin of the Amaterasu particle appears to be an empty part of the universe, which is baffling to scientists. This suggests the possibility of unknown astronomical phenomena or new physical origins beyond the Standard Model of particle physics.
There are several theories regarding the origins of these cosmic rays. For instance, the Pierre Auger Collaboration’s discovery indicates an origin outside our Milky Way galaxy, although the specific sources remain unknown. This discovery is significant, as it’s the first time in over a century since cosmic rays were first detected that the distant origin of these ultra-high-energy cosmic rays has been revealed.
Cosmic rays can be categorized into two types: galactic cosmic rays (GCR), originating beyond our solar system, and solar cosmic rays, primarily protons emitted by the sun. The study of these rays has revealed insights into the composition of cosmic rays and the abundance of elements like helium and hydrogen in the early universe.
The discovery of Amaterasu is not only a testament to the progress in cosmic ray research but also poses new challenges and questions for physicists. It opens up new avenues for understanding high-energy particle physics and the mysteries of the universe.