  We consider a spherically symmetric stationary problem in General Relativity,
including a black hole, inflow of normal and tachyonic matter and outflow of
tachyonic matter. Computations in a weak field limit show that the resulting
concentration of matter around the black hole leads to gravitational effects
equivalent to those associated with dark matter halo. In particular, the model
reproduces asymptotically constant galactic rotation curves, if the tachyonic
flows of the central supermassive black hole in the galaxy are considered as a
main contribution.
