Other
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusm.a32c..07l&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #A32C-07
Other
0399 General Or Miscellaneous
Scientific paper
Accretion is the main source of energy in many astrophysical objects, including different types of binary stars, binary X-ray sources, protoplanetary disks, and quasars and active galactic nuclei. The effective viscosity is the most speculative aspect of current accretion disk theory and modelling. The viscosity has the crucial effect of allowing matter with angular momentum to flow inward towards the central object, a compact star or black hole, and thereby release its gravitational binding energy. The atomic or plasma viscosity is too small by many orders of magnitude to be important. Shakura and Sunyaev proposed that the viscosity is due to turbulence in the disk. However, for standard disk models the Rayleigh criterion for stability is satisfied. Weak magnetic fields in ionized disks can cause instability and turbulence as discussed by Balbus and Hawley. However, in non-magnetized disks, such as disks in protoplanetary systems, other processes must be involved. A promising possibility is the instability of non-axisymmetric Rossby waves in a thin disks when there is a local maximum in the radial profile of a key function L(r) ≡ F(r) S2/Γ (r), where F-1 = ̂ zċ (∇x v) /Σ is the potential vorticity, S = P/Σ Γ is the entropy, Σ is the surface mass density, P is the vertically integrated pressure, and Γ is the adiabatic index (Lovelace et al. 1999). Reasons for the appearance of bumps in L(r) are discussed as well as nonlinear hydrodynamic simulations of disks by Li et al. (2001) which show the Rossby wave instability and the appearance of long-lived Rossby vortices in disks.
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