Black Holes in Non-flat Backgrounds: the Schwarzschild Black Hole in the   Einstein Universe
  As an example of a black hole in a non-flat background a composite static spacetime is constructed. It comprises a vacuum Schwarzschild spacetime for the interior of the black hole across whose horizon it is matched on to the spacetime of Vaidya representing a black hole in the background of the Einstein universe. The scale length of the exterior sets a maximum to the black hole mass. To obtain a non-singular exterior, the Vaidya metric is matched to an Einstein universe. The behaviour of scalar waves is studied in this composite model. 
K. Rajesh Nayak, M.A.H. MacCallum and C.V. Vishveshwara