A naked-eye star’s 50-year mystery is solved—its bizarre X-rays come from a hidden, feeding white dwarf.

Easily visible in the night sky within the constellation Cassiopeia, the star γ Cas has puzzled astronomers for more than 50 years. It produces X-rays with energies and temperatures far beyond what is expected from a typical massive star. New observations using the Resolve instrument aboard Japan’s XRISM space telescope have now traced this unusual emission to a white dwarf orbiting the star. This finding also confirms a long-theorized class of binary systems that had never been clearly identified. The study, led by researchers at the University of Liège, was published today (March 24) in Astronomy & Astrophysics.

What makes be stars like gamma cassiopeiae unique.