  In two previous publications$^{1,2}$, we have demonstrated that stationary
rotation of magnetized plasma about a compact central object permits an
enormous number of different MHD instabilities, with the well-known
magneto-rotational instability as just one of them. We here concentrate on the
new instabilities found that are driven by transonic transitions of the
poloidal flow. A particularly promising class of instabilities, from the point
of view of MHD turbulence in accretion disks, is the class of {\em trans-slow
Alfven continuum modes}, that occur when the poloidal flow exceeds a critical
value of the slow magnetosonic speed. When this happens, virtually every
magnetic/flow surface of the disk becomes unstable with respect to highly
localized modes of the continuous spectrum. The mode structures rotate, in
turn, about the rotating disk. These structure lock and become explosively
unstable when the mass of the central object is increased beyond a certain
critical value. Their growth rates then become huge, of the order of the Alfven
transit time. These instabilities appear to have all requisite properties to
facilitate accretion flows across magnetic surfaces and jet formation.[1] R.
Keppens, F. Casse, J.P. Goedbloed, "Waves and instabilities in accretion disks:
Magnetohydrodynamic spectroscopic analysis", Astrophys. J. {\bf 569},
L121--L126 (2002).[2] J.P. Goedbloed, A.J.C. Belien, B. van der Holst, R.
Keppens, "Unstable continuous spectra of transonic axisymmetric plasmas", Phys.
Plasmas {\bf 11}, 28--54 (2004).
