From [pov:6.7.12.6.1]:
BLACK_HOLE_WARP: warp { black_hole <Location>, Radius [BLACK_HOLE_ITEMS...] } BLACK_HOLE_ITEMS: strength Strength | falloff Amount | inverse | type Type | repeat <Repeat> | turbulence <Amount>
The minimal requirement is the black_hole
keyword followed by a vector
Location followed by a comma and a float Radius. Black holes effect all
points within the spherical region around the location and within the radius.
This is optionally followed by any number of other keywords which control how
the texture is warped.
The amount of displacement of the point is given by the formula
The keyword inverse
reverses the direction of the displacement.
The phrase repeat V
makes black holes at the lattice points specified
by the components of .
Andreas Kriegl 2003-07-23