  We study the harvesting of correlations by two Unruh-DeWitt static detectors
from the vacuum state of a massless scalar field in a background Vaidya
spacetime consisting of a collapsing null shell that forms a Schwarzschild
black hole (hereafter Vaidya spacetime for brevity), and we compare the results
with those associated with the three preferred vacua (Boulware, Unruh,
Hartle-Hawking-Israel vacua) of the eternal Schwarzschild black hole spacetime.
To do this we make use of the explicit Wightman functions for a massless scalar
field available in (1+1)-dimensional models of the collapsing spacetime and
Schwarzschild spacetimes, and the detectors couple to the proper time
derivative of the field. First we find that, with respect to the harvesting
protocol, the Unruh vacuum agrees very well with the Vaidya vacuum near the
horizon even for finite-time interactions. Second, all four vacua have
different capacities for creating correlations between the detectors, with the
Vaidya vacuum interpolating between the Unruh vacuum near the horizon and the
Boulware vacuum far from the horizon. Third, we show that the black hole
horizon inhibits \textit{any} correlations, not just entanglement. Finally, we
show that the efficiency of the harvesting protocol depend strongly on the
signalling ability of the detectors, which is highly non-trivial in presence of
curvature. We provide an asymptotic analysis of the Vaidya vacuum to clarify
the relationship between the Boulware/Unruh interpolation and the near/far from
horizon and early/late-time limits. We demonstrate a straightforward
implementation of numerical contour integration to perform all the
calculations.
