Cosmic dance through starlight: binary black holes could be spotted before waves wake the universe

Astronomers propose that gravitational lensing by pairs of merging supermassive black holes can magnify background stars into repeating, bright flashes as the black holes orbit, creating a rotating “caustic” pattern. Detecting these periodic light bursts would reveal binary supermassive black holes long before they merge and emit low‑frequency gravitational waves, enabling early multi‑messenger studies with future surveys from the Vera C. Rubin Observatory and the Roman Space Telescope, and later collaboration with LISA.