New Delhi: Researchers from Oxford University and the Max Planck Institute for Gravitational Physics have proposed a new way to detect hidden binary pairs
of supermassive black holes using gravitational lensing. These black holes bend and distort light from distant sources, creating bright images of stars from the same galaxy that lie behind the supermassive black hole. Binary pairs of supermassive black holes produce repeating flashes of lensed starlight, which can be registered by current and upcoming wide-field surveys. These bursts can also provide information on the properties of the black holes, allowing entirely new types of studies.
Binary pairs of supermassive black holes are formed when galaxies merge, but scientists have confidently observed only a few systems that are widely separated. Black hole binaries in tight orbits have not yet been measured. The researchers have suggested hunting down such binary black hole pairs using repeated flashes from individual stars lying behind the black holes. These binary systems play a crucial role in the evolution of the host galaxies, and are among the most powerful sources of gravitational waves in the universe. Future gravitational wave observatories will be able to probe such binaries directly, with the researchers now demonstrating how they can be detectable using existing and upcoming electromagnetic surveys.
Binary black hole pairs more likely to cause strong lensing
For a single supermassive black hole, the alignment for strong gravitational lensing has to be very precise, almost exactly along the line of sight. A binary pair of black holes produce a diamond shaped structure, known as a caustic curve. The stars along the curve can experience drastic magnification. The chances of gravitational lensing and flashes are increased in binary systems. As the binary system evolves over time, with the black holes gradually moving closer and closer, the caustic curve rotates and changes shape, sweeping across a large volume of stars behind. A paper describing the research has been published in Physical Review Letters.
