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Accretion disc viscosity: how big is alpha?

2007; Oxford University Press; Volume: 376; Issue: 4 Linguagem: Inglês

10.1111/j.1365-2966.2007.11556.x

1365-2966

A. R. King, J. E. Pringle, Mario Livio,

Stellar, planetary, and galactic studies

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