Astronomers have outlined a strategy to detect closely orbiting supermassive black hole binaries by searching for repeating flashes of magnified starlight caused by gravitational lensing.
Researchers from the University of Oxford and the Max Planck Institute for Gravitational Physics described the approach in a study published in Physical Review Letters. The method focuses on stars whose light is repeatedly amplified as it passes near the black hole pairs, which form after galaxy mergers. Dr. Miguel Zumalacárregui said supermassive black holes act as natural telescopes by bending passing light. Professor Bence Kocsis noted that a binary system creates a larger region where extreme magnification can occur compared to a single black hole. Graduate student Hanxi Wang led the research and explained that the orbiting black holes cause a caustic curve to sweep across background stars, producing predictable bursts of brightness. These patterns could allow astronomers to estimate black hole masses and orbital details. The Vera C. Rubin Observatory and Nancy Grace Roman Space Telescope are expected to help identify such events in coming years, potentially years before space-based gravitational wave detectors become available.