Supermassive black hole pairs can act like cosmic engines, pushing themselves out of the center of their home galaxies.
Most astronomers assume that heavy binary systems stay anchored in the dense center of a galaxy. This research shows that these binaries can actually propel their own center of mass in an outward spiral. This self-acceleration happens because of the asymmetry in how they interact with the surrounding gas and stars. The binary essentially kicks itself away from the galactic core without needing any outside force. This could explain why some massive black holes are found far from where they were expected to be.
Self-acceleration of Hardening Binaries
arXiv · 2605.00976
A Keplerian binary immersed in a bath of lighter particles hardens by ejecting them through gravitational slingshots. This process drives, for example, the evolution of supermassive black hole binaries following galaxy mergers, and has long been described with just two parameters: the hardening rate and the eccentricity growth rate. Here we show that the secular dynamics is substantially richer. Combining symmetry arguments with extensive three-body scattering experiments, we demonstrate that th