The ringdown-Hawking radiation connection in real and analogue black holes

In the usual picture of Hawking radiation, the emission is spontaneous; it is caused by nothing. In contrast, the radiation from the ringdown after a black-hole merger is caused dynamically by the fluctuations of the event horizon. We explore the possibility that Hawking radiation is also emitted dynamically by horizon fluctuations, in the form of quasinormal modes. In fact, we find that the fundamental, least-damped quasinormal mode is sufficient to radiate the entire Hawking spectrum of photons and gravitons, since the quasinormal mode spectrum is broadened by damping. The resulting Hawking spectra are accurate with no graybody factors. By comparing Hawking radiation to ringdowns, we find that the quantum fluctuations of the horizon should be on the order of 0.1 Planck lengths. We compare this result with predictions ranging over 60 orders of magnitude. Further support for the model is provided by a sonic black hole experiment, in which additional horizon fluctuations are seen to produce Hawking-like radiation.
Comment: 15 pages, 5 figures. This version discusses photons in addition to gravitons. More emphasis is placed on the Hawking spectra. The order of the sections is changed for clarity