Accretion disc viscosity: what do warped discs tell us?

Abstract

Standard, planar accretion discs operate through a dissipative mechanism, usually thought to be turbulent, and often modelled as a viscosity. This acts to take energy from the radial shear, enabling the flow of mass and angular momentum in the radial direction. In a previous paper we discussed observational evidence for the magnitude of this viscosity, and pointed out discrepancies between these values and those obtained in numerical simulations. In this paper we discuss the observational evidence for the magnitude of the dissipative effects which act in non--planar discs, both to transfer and to eliminate the non--planarity. Estimates based on the model by Ogilvie (1999), which assumes a small--scale, isotropic viscosity, give alignment timescales for fully ionized discs which are apparently too short by a factor of a few compared with observations, although we emphasize that more detailed computations as well as tighter observational constraints are required to verify this conclusion. For discs with low temperature and conductivity, we find that the timescales for disc alignment based on isotropic viscosity are too short by around two orders of magnitude. This large discrepancy suggests that our understanding of viscosity in quiescent discs is currently inadequate.

7 pages, no figures. MNRAS, in press

References in corpus (4)

• Accretion disc viscosity: how big is alpha?
• Tearing up the disc: how black holes accrete
• Warp diffusion in accretion discs: a numerical investigation
• The viscosity parameter alpha and the properties of accretion disc outbursts in close binaries

Cited by in corpus (28)

• The Kozai-Lidov Mechanism in Hydrodynamical Disks
• Tearing up a misaligned accretion disc with a binary companion
• On the physical nature of accretion disc viscosity
• Planet-disc evolution and the formation of Kozai-Lidov planets
• Warping a protoplanetary disc with a planet on an inclined orbit
• Dawes Review. The tidal downsizing hypothesis of planet formation
• Wave-like warp propagation in circumbinary discs II. Application to KH 15D
• The Kozai-Lidov Mechanism in Hydrodynamical Disks. II. Effects of binary and disk parameters
• Generalised warped disk equations
• A physical model for state transitions in black hole X-ray binaries
• The Kozai-Lidov Mechanism in Hydrodynamical Disks. III. Effects of Disk Mass and Self-Gravity
• The Evolution of Planet-Disk Systems That Are Mildly Inclined to the Orbit of a Binary Companion
• Misaligned accretion disc formation via Kozai-Lidov oscillations
• Radiation hydrodynamics models of Active Galactic Nuclei: Beyond the central parsec
• Kozai-Lidov Disc Instability
• Warp propagation in astrophysical discs
• The magnetospheric radius of an inclined rotator in the magnetically threaded disk model
• Global MHD Simulations of Accretion Disks in Cataclysmic Variables (CVs): II The Relative Importance of MRI and Spiral Shocks
• Probing the presence of planets in transition discs' cavities via warps: the case of TW Hya
• Observational signatures of linear warps in circumbinary discs
• Revisiting the structure and spectrum of the magnetic-reconnection-heated corona in luminous AGNs
• On the dynamics of low-viscosity warped discs around black holes
• Misaligned accretion on to supermassive black hole binaries
• Misaligned Accretion and Jet Production
• Accretion disc viscosity: a limit on the anisotropy
• Orbital dynamics of two circumbinary planets around misaligned eccentric binaries
• Modelling the observable behaviour of SXP 5.05
• Evidences of an innermost stable bound orbit predicted by general relativity from the amplitude of the twin-peak quasi-periodic oscillations