Figure 5

Figure 5: The physical setup for the scattering problem. A star of mass M has undergone spherically-symmetric collapse to form a black hole. The ingoing null worldtube 𝒩 lies outside the collapsing matter. Inside 𝒩 (but outside the matter) there is a vacuum Schwarzschild metric. Outside of 𝒩, data for an ingoing pulse is specified on the initial outgoing null hypersurface 𝒥 −. As the pulse propagates to the black-hole event horizon + ℋ, part of its energy is scattered to + ℐ.