Cosmic rays are extremely fast, charged particles that travel through space at nearly the speed of light. The Amaterasu particle was detected in 2021 by the Telescope Array experiment in the U.S. It is the second-highest-energy cosmic ray ever observed, carrying around 40 million times more energy than particles accelerated at the Large Hadron Collider. Such particles are exceedingly rare and thought to originate in some of the most extreme environments in the universe.