We clarify the concept of Keplerian circular motion of fluidsin the theory of general relativity, showing how it overlaps with as well as differs from the counterpart in the particle case. Applying the concept to the study of accretion disks, we prove a constraint on the sonic transition of accretion flows.

The motion of adiabatic jets propagating along the symmetry axis of a Kerr black hole is studied in the case where the outflowing matter possesses angular momentum. A simple parametrization is used for the cross-sectional area of the jets and the results applied to conical and paraboloidal jets. Inclusion of angular momentum in the outflowing material has the effect of shifting the critical point inward closer to the black hole, thus contributing to the radial acceleration of the flow. When the black hole is rotating, this inward shift is more pronounced for direct flows than retrograde ones: for a maximally rotating Kerr hole, the relative shift (with respect to a Schwarzschild black hole) varies from about 12% to 30% for the range of values of angular momentum considered. Rotation in the outflowing matter has the effect of reducing the mass outflow rate. Other parameters being the same, conical jets have their critical points considerably closer to the black hole than paraboloidal jets.

The disk-driven precession model, proposed originally for SS 433 by Sarazin et al. (1980), is applied to extragalactic radio jets. Byeresenting a statistical relationship between the precession period and optical luminosity fo the sources, it is shown that the observational evidence is in favor of the model.

Transonic motion of adiabatic jets from funnels of thick accretion disks around Kerr black holes is studied. Provided the matter at the bottom of the funnel possesses a high enough enthalpy, the location of the sonic point of the flow can be very close to its lower limit, and an extremely relativistic terminal velocity can be achieved.

Received September 10, 1984; accepted February 12, 1985 Summary. The fact that the adiabatic transonic accretion of rotating matter onto a black hole has non-unique, bimodal, solution was demonstrated previously only in terms of an approximate, Newtonian, model. Here the correct generalrelativistic equations are used to prove the bimodal character of accretion onto a Schwarzschild black hole.