  The density density correlation function is computed for the Bogoliubov
pseudoparticles created in a Bose-Einstein condensate undergoing a black hole
flow. On the basis of the gravitational analogy, the method used relies only on
quantum field theory in curved spacetime techniques. A comparison with the
results obtained by ab initio full condensed matter calculations is given,
confirming the validity of the approximation used provided the profile of the
flow varies smoothly on scales compared to the condensate healing length.
