Saul Teukolsky’s major contribution to general relativity was his publication on perturbations of a rotating black hole in the early 1970s. In 1973, Teukolsky derived linear equations describing the scalar, electromagnetic, gravitational, and neutrino field perturbations specifically for the Kerr metric, which depicts an electrically uncharged rotating black hole. Using perturbation theory for this case was more difficult than for the Schwarzschild metric, which lacks rotation. Teukolsky perturbed the Kerr black hole via the Newman-Penrose formalism, and the relevant perturbation equations could be decoupled and separated in terms of ordinary differential equations for the radial and angular coordinates. The resulting master equation is commonly known as the Teukolsky equation, which was derived in the Boyer–Lindquist coordinates, and can be written in the following form:
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