Understand
Hawking radiation originates from a "quantum atmosphere" around black holes, not necessarily from the vicinity of the horizon.
- We examine and discuss the properties of quantum atmospheres of asymptotically flat Reissner-Nordstr\"om black holes, which extends further and further away from the black hole as extremality is approached, though arguably it becomes indistinguishable from normal vacuum fluctuation at spatial infinity.
- In addition, following our previous findings on re-writing the Hawking temperature of a Kerr black hole in terms of a "spring constant", we generalize the same notion to the Reissner-Nordstr\"om case, which allows us to put a minimum size on the location where Hawking particles can be emitted near a black hole, which agrees with the stretched horizon.