Naked singularities and black hole Killing horizons

In this chapter, we study special photon orbits defined by means of Killing vectors and present a framework based on the properties of such null orbits. For concreteness, we restrict ourselves to the case of axially symmetric spacetimes describing either black holes with Killing horizons or naked singularities. The null-orbits framework is then applied to analyze properties of naked singularities and concepts of black hole thermodynamics.