Astronomers have discovered an activity cycle in another fast radio burst, potentially unearthing a significant clue about these mysterious deep-space phenomena.

Fast radio bursts, or FRBs, are extragalactic flashes of light that pack a serious wallop, unleashing in a few milliseconds as much energy as Earth’s sun does in a century. Scientists first spotted an FRB in 2007, and the cause of these eruptions remains elusive nearly a decade and a half later; potential explanations range from merging superdense neutron stars to advanced alien civilizations.