Self-propelled Pair of Black Holes ✎ express
Two black holes, orbiting each other, behave like a boat rowing with stars. Each passing star is flung away, like a stroke of an oar, and transfers momentum to the pair. For a long time, it was thought this simply brings the black holes closer. But new analysis has shown: by flinging stars unevenly, the system pushes itself sideways, spins, and tilts the orbit.
The reason is the shape of their path. The orbit is asymmetric, so the strokes are of different strength. The black holes begin to 'swim' away from the center of the galaxy, moving thousands of light-years away. This explains why supermassive black holes are sometimes found not at the center, and also changes their gravitational waves as they approach.
The most unexpected result: instead of damping, the orbit becomes increasingly elongated, like a lopsided oval. A similar orbital precession is seen in Mercury — explained by Albert Einstein — but here, instead of curved space, stellar 'oars' are at work.
A pair of black holes moves by flinging stars, like a boat rowing with oars.