Rotating Black Holes: Locally Nonrotating Frames, Energy Extraction, and Scalar Synchrotron Radiation

This paper outlines and applies a technique for analyzing physical processes around rotating black holes. The technique is based on the orthonormal frames of "locally nonrotating observers." As one application of the technique, it is shown that the extraction of the rotational energy of a black hole, although possible in principle (e.g., the "Penrose-Christodoulou" process), is unlikely in any astrophysically plausible context. As another application, it is shown that, in order to emit "scalar synchrotron radiation," a particle must be highly relativistic as seen in the locally nonrotating frame-and can therefore not move along an astrophysically reasonable orbit. The paper includes a number of useful formulae for particle orbits in the Kerr metric, many of which have not been published previously.