Turbulence in circumstellar disks

Abstract

We investigate the analogy between circumstellar disks and the Taylor-Couette flow. Using the Reynolds similarity principle, the analogy results in a number of parameter-free predictions about stability of the disks, and their turbulent transport properties, provided the disk structure is available. We discuss how the latter can be deduced from interferometric observations of circumstellar material. We use the resulting disk structure to compute the molecular transport coefficients, including the effect of ionization by the central object. The resulting control parameter indicates that the disk is well into the turbulent regime. The analogy is also used to compute the effective accretion rate, as a function of the disk characteristic parameters (orbiting velocity, temperature and density). These values are in very good agreement with experimental, parameter-free predictions derived from the analogy. The turbulent viscosity is also computed and found to correspond to an $\alpha$-parameter $2\times 10^{-4}<\alpha <2\times 10^{-2}$. Predictions regarding fluctuations are also checked: luminosity fluctuations in disks do obey the same universal distribution as energy fluctuations observed in a laboratory turbulent flow. Radial velocity dispersion in the outer part of the disk is predicted to be of the order of 0.1 km/s, in agreement with available observations. All these issues provide a proof of the turbulent character of the circumstellar disks, as well as a parameter-free theoretical estimate of effective accretion rates.

Accepted for publication in Astronomy and Astrophysics, 13 pages

References in corpus (7)

• Accretion Disks around Young Objects. I. The Detailed Vertical Structure
• Magnetorotational Instability in Protoplanetary Disks. II. Ionization State and Unstable Regions
• The ionization fraction in alpha-models of protoplanetary disks
• An hydrodynamic shear instability in stratified disks
• Spectra and Line Profiles of FU Orionis Objects: Comparisons Between Boundary Layer Models and Observations
• Magnetic instability in a sheared azimuthal flow
• Can FU Orionis Outbursts Regulate the Rotation Rates of T Tauri Stars?

Cited by in corpus (12)

• High Reynolds number Taylor-Couette turbulence
• On the relevance of subcritical hydrodynamic turbulence to accretion disk transport
• Empirical Constraints on Turbulence in Protoplanetary Accretion Disks
• Influence of global rotation and Reynolds number on the large-scale features of a turbulent Taylor-Couette flow
• Angular momentum transport and turbulence in laboratory models of Keplerian flows
• Analysis of the dust evolution in the circumstellar disks of TTauri stars
• Momentum transport in Taylor-Couette flow with vanishing curvature
• Electromagnetic streaming instabilities of magnetized accretion disks with strong collisional coupling of species
• On the pressure of collisionless particle fluids. The case of solids settling in disks
• Observation of aerodynamic instability in the flow of a particle stream in a dilute gas
• Laboratory modeling of MHD accretion disks
• Angular Momentum Transport by Keplerian Turbulence in Liquid Metals