It looks like it steals energy from an object in motion, in this case a black hole. (Presumably because this is a dense object so you can get closer to it.) Ex

It looks like it steals energy from an object in motion, in this case a black hole. (Presumably because this is a dense object so you can get closer to it.) Existing satellite slingshot maneuvers steal energy from the thing they slingshot around -- every satellite that slingshots off earth steals a very, very small amount of energy from the earth. The closer you get to the center of Earth's mass, the more energy you can steal. It's just that in Earth's case there's all this "atmosphere" and "lithosphere" garbage preventing you from snuggling up right close to the center. With a black hole, all that stuff is compressed, so you can get closer and steal some of its kinetic energy. (If I understand the concept correctly.)