Figure 14: Escape cones in the Schwarzschild metric, for five values of . For an observer at radius , light sources distributed at a radius with and illuminate a disk whose angular radius is given by Equation (107). The boundary of this disk corresponds to light rays that spiral towards the light sphere at . The disk becomes smaller and smaller for . Figure 9 illustrates that the notion of escape cones is meaningful for any spherically symmetric and static spacetime where has one minimum and no other extrema [253]. For the Schwarzschild spacetime, the escape cones were first mentioned in [249, 224], and explicitly calculated in [319]. A picture similar to this one can be found, e.g., in [54].