  In this thesis, we have studied the information loss paradox in detail. As a
first step, we have derived the main results of quantum field theory in a
curved background. We have discussed the case of the free scalar Klein-Gordon
field and concluded with a derivation of the so-called Unruh effect in
Minkowski spacetime. After giving a brief survey of necessary concepts, such as
surface gravity and the redshift factor, we have applied them along the results
from the Unruh effect to derive the temperature of Hawking radiation. Later, we
have used the formalism of QFT in curved spacetime to rigorously obtain the
distribution of the radiation, considering a black hole formation process.
Thus, we have focused on the quantum mechanical states of the radiation quanta
and the mass in the black hole, showing that at first order plus small
corrections (condition needed to neglect effects of quantum gravity in normal
physics) the Hawking conclusion of mixed states/remnants holds. Finally, we
have presented some of the principal results of the recent study of asymptotic
symmetries and the $BMS_4$ symmetry group. We have concluded presenting some
ideas relating the gravitational memory effect with the supertransformations
and the soft hair carrying the black holes.
