Transmagnetosonic Accretion in a Black Hole Magnetosphere

We present the critical conditions for hot trans-fast magnetohydrodynamical(MHD) flows in a stationary and axisymmetric black-hole magnetosphere. Toaccrete onto the black hole, the MHD flow injected from a plasma source withlow velocity must pass through the fast magnetosonic point after passingthrough the ``inner'' or ``outer'' Alfven point. We find that a trans-fast MHDaccretion solution related to the inner Alfven point is invalid when thehydrodynamical effects on the MHD flow dominate at the magnetosonic point,while the other accretion solution related to the outer Alfven point is invalidwhen the total angular momentum of the MHD flow is seriously large. When bothregimes of the accretion solutions are valid in the black hole magnetosphere,we can expect the transition between the two regimes. The variety of thesesolutions would be important in many highly energetic astrophysical situations.Comment: 27 pages, 12 figures, accepted to Ap