Astrophysicists have theorized for decades that the mysterious, ultrahigh-energy cosmic rays (UHECRs) detected on Earth could come from active galactic nuclei (AGNs), the supermassive black holes at the centers of galaxies. The particle acceleration mechanism, however, has been unclear. Now a team of researchers from SLAC National Accelerator Laboratory has used the ALCF's Mira supercomputer to perform simulations of unprecedented size to propose a new mechanism.