50-Year Cosmic Mystery Solved: Hidden White Dwarf Revealed as Source of Gamma-Cas X-Rays

For half a century, a bright star in Cassiopeia emitted X-rays so fierce they seemed to mock every explanation astronomers could offer. Now, an international team wielding the precision of the XRISM space mission has traced that fierce radiation to its true source: a hidden white dwarf, quietly stealing matter from its companion and heating it to temperatures that rival the cores of the most violent cosmic events. The mystery that began with a peculiar spectral line in 1866 and deepened in the 1970s has at last found its answer — not in magnetic chaos, but in the ancient, patient act of one dy