Accretion disc viscosity: how big is alpha?

By A. King, J. E. Pringle, M. Livio. 2007

351 citations recorded by the source corpus.

We consider observational and theoretical estimates of the accretion disc viscosity parameter a. We find that in thin, fully ionized discs, the best observational evidence suggests a typical range a ∼ 0.1-0.4, whereas the relevant numerical simulations tend to derive estimates for a which are an order of magnitude smaller. We discuss possible reasons for this apparent discrepancy.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/212bbbd485b4fc64d7eb8346a086f21e802b2ff0

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In Astronomy and Astrophysics

1. A. Tchekhovskoy
2. B. Metzger
3. Ramesh Narayan
4. C. Mordasini
5. E. Quataert
6. Y. Alibert
7. J. McKinney
8. J. Farihi

Citations in the corpus

• General relativistic magnetohydrodynamic simulations of magnetically choked accretion flows around black holes (2012, result): “Our poloidal and toroidal field simulations have αeff ∼ 0.2–1 (which indicates the actual effective viscous timescale) that is large enough to be consistent with observations (King et al. 2007).”
• On the charge of the Galactic centre black hole (2018, background): “When the viscosity parameter α is of the order of 0.1 (King et al. 2007; Lasota 2016), the viscous timescale is tvis ≈ 10tdyn.”
• Black hole mergers: can gas discs solve the ‘final parsec’ problem? (2009, neutral): “We takeα = 0.1 throughout (King et al. 2007).”
• Formation and Evolution of Compact-object Binaries in AGN Disks (2019, methodology): “In the inner region, we adopt the α model for angular momentum transport, in which the alpha parameter is αSS=0.1 (King et al. 2007; Bai & Stone 2013).”
• Rapid and Bright Stellar-mass Binary Black Hole Mergers in Active Galactic Nuclei (2016, methodology): “We adopt the viscosity parameter α = 0.3 (King et al. 2007).”
• Strange messenger: A new history of hydrogen on Earth, as told by Xenon (2018, methodology): “ factor . This scaling is used in the ubiquitous -disk model of astrophysical accretion disks, with the scale length equated to the scale height. The models work best with of the order of 0.1 to 0.4 (King et al, 2007). Using this prescription, a turbulent K0 zz might be of the order of 1 110 9 4 10 ”
• Pseudo-viscous modelling of self-gravitating discs and the formation of low mass ratio binaries (2009, methodology): “The value of α delivered by the MRI is a fluctuating quantity, whose time average has been reported over a wide range, mainly in the domain < 0.01 (see discussion in King et al 2007); here we adopt αMRI = 0.01.”
• Circumstellar Debris and Pollution at White Dwarf Stars (2016, background): “In either case, if sufficient mass in a fully ionized disk of gas results (so that the MRI operates), then standard α disk accretion (King et al., 2007) will result, where rates can easily exceed 1011 g s−1 by a few orders of magnitude.”
• Time-dependent models of accretion discs formed from compact object mergers (2008, background): “However, there is observational evidence for α ∼ 0.1 in a number of astrophysical disks (King et al. 2007); we thus doubt that tthick is large enough to coincide with the onset of observed flaring.”
• POLLUTION OF SINGLE WHITE DWARFS BY ACCRETION OF MANY SMALL ASTEROIDS (2008, background): “As discussed by King et al. (2007), empirical estimates of α for thin, fully ionized disks are between 0.1 and 0.4, but theoretical simulations yield values of α that are at least an order of magnitude lower.”
• Classical Be stars (2013, background): “…galactic nuclei, the elementary physical processes of gravity, radiative transfer, and radiative pressure have much in common (Woosley 1993; Balbus and Hawley 1998; Hartmann et al. 1998; Lubow et al. 1999; Nelson et al. 2000; King et al. 2007, just to name a few works on disks in various contexts).”
• Extrasolar planet population synthesis - II. Statistical comparison with observations (2009, background): “Third, at least one of the parameters, α, can only be varied within about one order of magnitude as observational constraints exist (King et al. 2007).”