Black Hole Propulsion as Technosignature

If it can reach a black hole binary, it has gained an essentially free source of energy for continued operations in moving objects to relativistic speeds. During departure, one is stealing energy from the black binary, which causes the separation between the two dead stars to shrink slightly via the loss of gravitational potential energy. Kipping says he has not run the numbers on this yet, but from the work so far be believes that a spacecraft could work with angles as high as 20 degrees out of the plane of the binary orbit and still reach an acceleration equal to that of the black hole.

Source: www.centauri-dreams.org