Scattering by black holes

Publisher Summary This chapter discusses possible diffraction effects and resonances, and some of the peculiarities of the black hole problem. The quasinormal modes provide a unique way of identifying black holes and deducing their mass and rate of rotation. Given this, it is instructive to have simple approximations of the most important mode frequencies. One can readily arrive at such expressions by considering that the black hole problem is essentially one of scattering off a single potential peak. It is commonly accepted that scattering resonances arise for energies close to the top of a potential barrier. The Hawking radiation emitted by a black hole is not produced by the process of collapse, but is a feature of the field vacuum state in the new space-time, which now contains a black hole. The chapter concludes with an introduction to Kerr black hole.