  We investigate the occurrence chaos in the escape of test particles moving in
the field of a Schwarzschild black hole surrounded by an external halo. The
motion of both material particles and zero rest mass particles is considered.
The chaos is characterized by the fractal dimension of boundary between the
basins of the different escapes, which is a topologically invariant
characterization. We find chaos in the motion of both material particles and
null geodesics.
