XRISM identifies gamma Cas X-ray origin, solving a 50-year-old stellar mystery

Visible to the naked eye in the constellation Cassiopeia, the star γ Cas has intrigued astrophysicists for half a century. It emits X-rays of an intensity and temperature incompatible with those that one would expect from an ordinary massive star. Observations, carried out using the Resolve instrument on board the Japanese XRISM telescope, now make it possible to attribute this emission to the white dwarf orbiting γ Cas. It also confirms the existence of a family of binary systems whose existence was long predicted but never identified.