On dynamics of nonmagnetic accretion disks
  Axisymmetric accretion disks in vicinity of a central compact body are
studied. In the case of non-viscous disk it is proven that all solutions for
the midplane circular velocity are unstable. Hence, the pure hydrodynamic
turbulence in accretion disks is possible. It is disproved the well-known
arguments that an inviscid accretion disk must be sub-Keplerian. It is also
demonstrated that the regular asymptotic solutions, often used in astrophysics,
can lead to erroneous conclusions. It is proven that a laminar viscous disk can
be approximated with a great precision by the vortex motion. Assuming that a
turbulent gas tends to flow with minimal losses, we have shown that a turbulent
disk tends to be Keplerian.
