Researchers at Yale University have been trying to understand how merging supermassive black holes can overcome the final-parsec problem, where they stall before merging. Different theories propose various solutions, including stars interacting with the black holes to extract angular momentum or a third black hole joining the system. Some scientists also suggest that self-interacting dark matter could play a role in speeding up the merger process. The European Space Agency's LISA spacecraft is expected to provide more answers by detecting strong gravitational waves emitted by merging supermassive black holes.

Source: https://www.quantamagazine.org/how-do-merging-supermassive-black-holes-pass-the-final-parsec-20241023/