Do magnetized winds or turbulence drive accretion in protoplanetary disks? · revision history
Revision 1
Accepted · first revision · record
- Title
- Do magnetized winds or turbulence drive accretion in protoplanetary disks?
- Plain
- Gas in a disk can only fall onto the star if it loses its spin, either by passing it outward through turbulent stirring or by carrying it away in a magnetized wind (gas flung off the disk surface along magnetic field lines). Measurements suggest the disks are too calm for turbulence to do the job, but this is not settled.
- Precise
- Classical T Tauri disks accrete at $\mathrm{mdot} \sim 10^{-9}-10^{-7}\ M_{\mathrm{sun}}/\mathrm{yr}$; a turbulent-viscosity model needs $\alpha \sim 10^{-3}-10^{-2}$, while non-ideal MHD (low ionization, Ohmic, ambipolar and Hall effects) suppresses the magnetorotational instability over much of $1-30\ \mathrm{AU}$. Determine the fraction of the angular-momentum flux carried by magnetized disk winds versus radial turbulent transport as a function of radius, using nonthermal molecular line widths, dust vertical settling, and measured wind mass-loss rates. The answer is the radial profile of the wind-to-turbulent torque ratio, or a demonstration that one channel dominates at $1-100\ \mathrm{AU}$ in typical disks.
- Settled by
- ALMA turbulence and settling measurements combined with spatially resolved wind tracers (JWST molecular hydrogen and forbidden-line imaging) for the same disks, compared with the measured stellar accretion rates.
- Kind
- well-posed
- Answer type
- identification
- References
- (empty)
- Literature status
- contested
- Status note
- ALMA line-width and dust-settling studies of 2015-2020 find $\alpha$ below about $10^{-3}$ in most disks examined, which favors wind-driven accretion, but turbulence with $\alpha$ of order 0.1 was reported in DM Tau (Flaherty et al. 2020).
- Posed since
- (empty)