  We study the perception of the radiation phenomena of Hawking radiation and
Unruh effect by using two main tools: the Unruh-DeWitt detectors and the
effective temperature function (ETF), this last tool based on Bogoliubov
transformations. Using the Unruh-DeWitt detectors we find an adiabatic
expansion of the detection properties along linear trajectories with slowly
varying acceleration in Minkowski, which allows us to calculate the spectrum
detected, finding the thermal spectrum as the zeroth order contribution. Using
the ETF we study the perception of Hawking radiation by observers following
radial trajectories outside a Schwarzschild black hole. One of the most
important results is that, in general, free-falling observers crossing the
event horizon do detect some radiation, even when the field is in the Unruh
vacuum state, due to a Doppler blue-shift that diverges at the horizon. We give
a general expression for the ETF, which has a clear interpretation in terms of
well-known physical phenomena. We discuss which contribution to the perception
comes from the radiation emitted by the black hole, and which contribution is
due to the Unruh effect caused by the movement of the observer. We conclude
that the Unruh effect is not only due to the observer's proper acceleration and
cannot even be defined locally, but is due to the observer's acceleration with
respect to the asymptotic region. We apply the ETF to the analysis of different
physical situations, in particular to a possible buoyancy scenario near the
horizon due to Hawking radiation pressure. Finally, we propose a non-stationary
vacuum state, which we call pulsating vacuum, for the radiation field outside a
stellar object hovering closely to form an event horizon. In this vacuum state,
we get nearly Hawking radiation emitted by the object, while avoiding the known
problems of the information paradox and the trans-planckian problem.
