The most powerful cosmic ray since the Oh-My-God particle puzzles scientists

Scientists have detected the most powerful cosmic ray seen in more than three decades. But the exact origin of this turbocharged particle from outer space remains a mystery, with some suggesting that it could have been generated by unknown physics.

The puzzling cosmic ray had an estimated energy of 240 exa-electron volts (EeV; 1018 volts), making it comparable to the most powerful cosmic ray ever detected, aptly named the Oh-My-God particle, which measured at around 320 EeV when it was discovered in 1991. The findings were published today in Science1.

“It’s amazing because you have to think of what could produce such high energy,” says Clancy James, an astronomer at Curtin University in Perth, Australia.

A cosmic ray, despite its name, is actually a high-energy subatomic particle — often a proton — that zips through space at close to the speed of light. In their ultra-high energy form, cosmic rays have energy levels that exceed one EeV, which is around one million times greater than those reached by the most powerful human-made particle accelerators. Cosmic rays with energies of more than 100 EeV are rarely spotted — fewer than one of these particles arrive on each square kilometre of Earth each century.