Evrim Yazgin
Cosmos science journalist
Astronomers have observed the second largest cosmic ray ever detected. Physicists cannot comprehend where in the universe such an energetic ray could come from. The particles within it shouldn’t exist.
Cosmic ray 101
Cosmic rays’ highly energetic streams of subatomic particles shoot through the universe at nearly the speed of light. They are made up of about 89% protons (hydrogen nuclei), 10% helium nuclei and the remaining 1% is made up of heavier nuclei (all the way to uranium on the Periodic Table).
When these speedy nuclei collide with atoms in Earth’s upper atmosphere, new particles are created. In fact, these interactions led to the discovery of a slew of particles outside the atom: positrons (the first identified antimatter particle), muons, pions, kaons and others.
These particle streams are constantly raining down on earth. Cosmic rays strike every square centimetre on Earth every minute. Some might come from supernovae – the violent death of a massive star, the largest explosion known to science.
Occasionally, cosmic rays are detected with such high energy particles that physicists are completely stumped.
Oh My God (particle)
In 1991, the highest energy cosmic ray ever was detected. It was dubbed the “Oh-My-God” particle.
Nothing in the galaxy had the power to produce it and it had more energy than was theoretically possible for a cosmic ray travelling from another galaxy.
The Oh-My-God particle had 320 exa-electron volts (320 EeV; 320 with 18 zeroes after it) of energy.
Cosmic rays rarely reach energies higher than 1 EeV – about a million times more than the energy generated by the most powerful particle accelerators made by humans.
No cosmic ray had come close to the Oh-My-God particle, until now.
“Amaterasu” particle
On 27 May 2021, a cosmic ray measuring 244 EeV struck the Telescope Array experiment which covers 700 km2 in Utah, US. The ultra high-energy cosmic ray was named “Amaterasu,” after the Shinto sun goddess said to have been instrumental in the creation of Japan.
A single Amaterasu particle contains an amount of energy equivalent to dropping a brick onto your toe from your waist.
The discovery is detailed in a paper published in the journal Science.
“No promising astronomical object matching the direction from which the cosmic ray arrived has been identified, suggesting possibilities of unknown astronomical phenomena and novel physical origins beyond the Standard Model,” says study leader Associate Professor Toshihiro Fujii from Osaka Metropolitan University.
Cosmos is a not-for-profit science newsroom that provides free access to thousands of stories, podcasts and videos every year. Help us keep it that way. Support our work today.