According to this Bigthink article which cites this paper all massive objects emit Hawking radiation because they curve spacetime.
But I thought Hawking radiation is the time reversal of a particle falling into a black-hole. Time-reversal is necessary for the laws of thermodynamics to hold; since horizons are perfect absorbers they must also be perfect black-body emitters.
A transparent gas cloud bends spacetime but it cannot absorb light. So how can it emit Hawking radiation? There is no absorption process that can be time-reversed. The article raises similar objections but does not provide a clear answer.
