Like most objects in the universe (planets, stars, asteroids, and other compact objects), black holes rotate. We refer to this property as “spin” or, more formally, its “angular momentum” about its axis of rotation. By looking for light distortions in X-rays streaming off material near black holes, researchers can gain information about their spins. The accretion disk also spins, and not necessarily in the same direction as the black hole. Astronomy: Roen Kelly, after NASA/JPL-Caltech