The Schwarzschild spacetime is for electromagnetic waves like a nonuniform
medium with a varying refraction index. A fraction of an outgoing radiation
scatters off the curvature of the geometry and can be intercepted by a gra
vitational center. The amount of the intercepted energy is bounded above by
the backscattered energy of an initially outgoing pulse of electromagnetic
radiation, which in turn depends on the initial energy, the Schwarzschild
radius and the pulse location. Its magnitude depends on the frequency spect
rum: ii; becomes negligible in the short wave limit but can be significant
in the long wave regime.