Exploring quantum fields in rotating black holes

Since astrophysical black holes are expected to be rotating, one would like to study quantum fields on such spacetimes. For linear theories, one of the biggest difficulties lies in identifying and constructing physically reasonable and well-motivated states for the quantum theory. In this talk, we discuss one example of such a state for rotating black holes, the Unruh state. We will detail its construction, as well as the proof for it being physically reasonable. If time permits, we will mention some applications of the Unruh state for the exploration of quantum effects on black hole spacetime.