Fluctuation on a Schwarzschild black hole
When a relativistic perturbation is given to the horizon of a Schwarzschild black hole, a new supersurface near the horizon will be obtained. Using the gravitational anomaly method proposed by Robinson and Wilczek, Hawking radiation from this new supersurface is calculated. It is found that the first law of thermodynamics can also be constructed successfully on this supersurface. The expressions of the characteristic position and temperature are very similar to the previous results for the event horizon of a Vaidya black hole. Comparing with the Vaidya black hole, we conclude that Hawking radiation and the thermodynamics of a Vaidya black hole should be indeed constructed at the apparent horizon instead of the event horizon.