SPHERICAL SCALAR WAVES AND GRAVITY - REDSHIFT AND BACKSCATTERING

This paper investigates the interaction of a spherically symmetric mas sless scalar field with a strong gravitational field. It focuses on th e propagation of waves in regions outside any horizons. The two factor s acting on the waves can be identified as a redshift and a backscatte ring. The influence of backscattering on the intensity of the outgoing radiation is studied and rigorous quantitative upper bounds obtained. These show that the total flux may be decreased if the sources are pl aced in a region adjoining an apparent horizon. Backscattering can be neglected in the case 2m(())/R much less than 1, that is when the emit ter is located at a distance from a black hole much larger than the Sc hwarzschild radius. This backscattering may have noticeable astrophysi cal consequences.