Is it possible to deduce that a blackhole must have something akin to Hawking radiation due to the 2nd Law of Thermodynamics? Let us consider for now a purely classical blackhole. The event horizon is effectively a 'light diode' in that if light can pass through in a particular direction, it can not pass through in the opposite direction. Therefore if we place a (again, purely classical) blackhole in a vaccuum with a thermal bath of photons, it will take away thermal energy from the surrounding area, creating a thermal gradient in the bath ... which in turn would allow energy to be extracted from the thermal bath. This seems to violate the 2nd Law of thermodynamics, unless we consider (still purely classical) blackholes to be objects of zero kelvin temperature with infinite heat capacity. Since we can classically consider the formation of a blackhole from a collapse of finite temperature material, that seems to be an invalid consideration unless the creation of a blackhole is violently endothermic. Since blackholes of mass M (and no spin or charge) classically settle on only one solution, their entropy would be zero so we can't satisfy the 2nd law via the usual way endothermic reactions do. It seems to me that the 2nd law of thermodynamics alone demands that blackholes have thermal radiation. I don't think one could derive much or any specifics, let alone the details that is Hawking radiation. Yet it appears blackhole evaporation is necessary for the 2nd Law of Thermodynamics? Does anyone have some comments on this? I believe I remember reading a similar argument in a 'undergraddy/simple math intro gr' book, but can't find it currently. If you could point me to a more indepth textbook that discusses this, that would be wonderful.