For fifty years, astronomers couldn't understand the powerful X-rays from the star Gamma Cassiopeiae. They suspected an invisible companion, but had no proof. Japan's XRISM telescope, armed with high-resolution spectroscopy, caught tiny shifts in the emission lines. Those oscillations precisely matched the motion not of the main star, but of its tiny partner.

It turned out to be a white dwarf – a superdense stellar leftover whose maximum mass was worked out by Chandrasekhar. Gas from the big star streams toward the dwarf and, like water down a drain, spirals into a searing hot disk. There it heats to millions of degrees, giving off that very X-ray glow. The find is like solving a magic trick: we finally see where the matter disappears.

Such pairings, it turns out, aren't rare: one in ten massive stars with a disk conceals a white dwarf. This helps us grasp how supernovae and neutron stars are born. The cosmos is teeming with invisible drains, gobbling up their neighbors.