  A highly accurate multi-domain spectral method is used to study axially
symmetric and stationary spacetimes containing a black hole or disc of dust
surrounded by a ring of matter. It is shown that the matter ring can affect the
properties of the central object drastically. In particular, by virtue of the
ring's frame dragging, the so-called Komar mass of the black hole or disc can
become negative. A continuous transition from such discs to such black holes
can be found.
