For half a century, astronomers puzzled over the nature of the powerful X-ray emission from Gamma Cassiopeiae — a bright beacon in its constellation whose X-ray glow didn't fit models of single stars. An invisible companion was suspected, but direct evidence was lacking. The breakthrough came from Japan's XRISM X-ray telescope, equipped with high-resolution spectroscopy — a technique that splits radiation into ultra-fine spectral lines and tracks the slightest frequency shifts. The telescope detected periodic oscillations in these lines that precisely matched the orbital motion not of the main star but of its tiny partner.

The companion turned out to be a white dwarf — an ultra-dense stellar remnant that has exhausted its thermonuclear fuel. Its maximum mass, above which the object collapses, was calculated by Subrahmanyan Chandrasekhar, and this limit bears his name. In a pair with a massive star, the white dwarf acts like a cosmic 'vacuum cleaner': gas from the surface of the big star flows toward the dwarf and, like water in a funnel, spirals into an accretion disk. In this disk, matter is heated by friction to millions of degrees, emitting the very X-ray glow that had baffled scientists for decades. The discovery is akin to solving a magic trick: we finally see where the matter disappears and realize that the X-ray light is born not in the star itself but in the blazing 'whirlpool' around the dwarf.

XRISM's spectroscopy not only identified the companion but also allowed an estimate of how common such systems are. It turns out that one in ten massive stars with a circumstellar disk hides a white dwarf. This discovery sheds light on the evolutionary paths of binary systems and helps explain how supernovae, grand explosions, and neutron stars — ultra-dense objects formed in collapses — are born. The cosmos is full of invisible 'funnels' devouring their neighbors, and now we have a tool to peer into their abyss.