Scientific researchers in Japan have made a groundbreaking discovery—the existence of an ultra-high-energy particle on Earth. These particles have been perceived to emerge from the Local Void, an empty area of space bordering the Milky Way galaxy where nothing is known to be present. This extraordinary particle has been named as ‘Amaterasu’ after Amaterasu Omikami, the goddess of the Sun in the Japanese mythology.
Telescope Array Experiment
The ultra-high-energy cosmic ray was captured by the Telescope Array experiment on May 27, 2021. This is an unconventional telescope which is spread across Utah’s dry Bonneville lake bed in North America, located in the desert region. This provides ideal atmospheric conditions in two ways: the dry air is crucial as humidity would absorb the ultraviolet light necessary for detection of cosmic rays; and the region’s dark skies are essential, as light pollution would create too much noise and obscure the cosmic rays. This specialised cosmic ray detector consists of 507 scintillator surface stations, covering an expansive detection area of 700 square kilometres in Utah. The project started in 2008, and has observed more than 30 ultra-high-energy cosmic rays. The project is made up of instruments which collects the particles produced when cosmic rays collide with charged particles in the air. Instruments including the Telescope Array Observatory could detect cosmic rays that reach earth’s atmosphere. As these particles travel, their flight path twist and turn against the electromagnetic fields through the cosmic microwave background, below a certain energy threshold.
About Amaterasu
Astronomer Toshihiro Fuji of the Osaka Metropolitan University in Japan observed some distinctive signals while he was conducting a routine data check at the Telescope Array Project in Utah. These signals indicated that there was a super-energetic substance that had smashed into the facilities’ detectors. Fuji was sceptical about the high-energy particle as its measurements pointed that it was ultra-cosmic rays. He studied the signals along with his team and published a paper, titled ‘An extremely energetic cosmic ray observed by a surface detector array’, in November 2023, in the journal Science.
According to astronomers, the following could be the reasons for the enigmatic origin of the particle:
- It could be from a source that has not been identified as of yet.
- It might have been magnetically deflected much higher than what current models predict.
- Scientists might need to rewrite their incomplete understanding of high-energy particle physics.
Characteristics of Amaterasu
The Amaterasu cosmic ray particle has an energy level exceeding 240 exa-electron volts (EeV). This particle is million times more powerful than the particles produced by the Large Hardon Collider, which is the world’s largest and most powerful particle accelerator. Amaterasu’s energy is second to the ‘Oh-My-God’ particle, a high-energy cosmic ray particle with 320 EeV, detected in 1991.
However, the researchers could not find the source of the cosmic rays. They presume that Amaterasu particle would have travelled through space smoothly since it did not bounce off magnetic fields, such as low-energy cosmic rays. According to the calculation of the researchers, the ray seems to have come from a void-like region.
Cosmic Rays
Cosmic rays, discovered by Victor Hess, in 1912, are energetic subatomic particles or cluster of particles produced by naturally occurring particle accelerators in outer space. He was awarded the Nobel Prize in Physics for the discovery. The rays move through space almost at the speed of light and consists of charged particles (electrons, protons, and atomic nuclei). They originate from various sources, including the Sun, from outside the Solar System, within our galaxy as well as from distant galaxies. Cosmic rays produce extensive cascades of subatomic particles and ionised nuclei. Some of these particles reach the surface of the Earth. However, majority of it is deflected into the space. Most of the energy of the cosmic rays is absorbed by the Earth’s atmosphere, allowing only a small fraction of it reaching the ground level.
The detection of the Amaterasu particle opens new avenues for understanding the cosmos and challenges of existing paradigms in high-energy physics. As scientists continue to unravel the mysteries of cosmic rays, the Telescope Array Project remains at the forefront, probing the depths of space for further revelations.
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