On dynamics of nonmagnetic accretion disks

TL;DR

This paper investigates the stability and dynamics of nonmagnetic accretion disks, demonstrating that pure hydrodynamic turbulence is possible and that turbulent disks tend to be Keplerian, challenging previous assumptions about inviscid disks.

Contribution

It proves the instability of solutions in non-viscous disks, discredits the sub-Keplerian argument for inviscid disks, and shows turbulent disks approximate vortex motion and tend to be Keplerian.

Findings

Pure hydrodynamic turbulence is possible in non-viscous disks.

Inviscid accretion disks are not necessarily sub-Keplerian.

Turbulent disks tend to be Keplerian.

Abstract

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.