Physical Effects in the Gravitational Field of a Black Hole

Abstract

In this chapter we continue the discussion of the effects of interaction between classical particles and fields and black holes. 1 Let us begin by analyzing the efficiency of energy extraction from black holes. Recall that although a black hole is by definition a region of no escape for material bodies and light rays, situations are possible in which energy can be extracted via certain physical processes. We will see later that this energy is extracted from a field connected to the black hole and surrounding it. Thus, extraction is possible if the black hole rotates or is charged. We already discussed two examples of such processes; namely, the Penrose process (Section 6.2.3) and superradiance (Section 4.8.2). In this section, we establish some general restrictions on the possible efficiency of this kind of process.