We have used the analogy between gravitational systems and nonhomogeneous fluid flows to calculate the density-density correlation function of an atomic Bose-Einstein condensate in the presence of an acoustic black hole. The emission of correlated pairs of phonons by Hawking-like process results into a peculiar long-range density correlation. Quantitative estimations of the effect are provided for realistic experimental configurations.

It is known that the Einstein field equations in five dimensions admit more general spherically symmetric black holes on the brane than four-dimensional general relativity. We propose two families of analytic solutions (with $g_{\mathrm{tt}}\ne -g_{\mathrm{rr}}^{-1}),$ parametrized by the Arnowitt-Deser-Misner mass and the parametrized post-Newtonian parameter $\beta ,$ which reduce to Schwarzschild for $\beta =1.\mathrm{}$ Agreement with observations requires $|\beta -1|\sim |\eta |\ll 1.$ The sign of $\eta$ plays a key role in the global causal structure, separating metrics which behave like Schwarzschild $(\eta <0)$ from those similar to Reissner-Nordström spare-time $(\eta >0).\mathrm{}$ In the latter case, we find a family of black hole space-times completely regular.