They are the zestiest bits of matter in the universe. They can zing through space for millions of years at essentially the speed of light and with 100 million times the energy produced by the biggest particle accelerators on the earth, before crashing occasionally into Earth’s atmosphere and dying in a spray of microscopic fluff.

Since these ultrahigh-energy cosmic rays, as they are known, were first glimpsed in 1963, physicists and astronomers have scratched their heads wondering where they came from and what gargantuan process could produce such energies — wondering, even, if they were real.