How do T Tauri stars accrete

TL;DR

This paper suggests that low-viscosity hydrodynamic turbulence can explain observed accretion rates in T Tauri stars' protoplanetary discs, aligning with surface density estimates and offering an alternative to magnetic wind-driven models.

Contribution

It demonstrates that low viscosities consistent with hydrodynamic turbulence can account for accretion rates and disc lifetimes, challenging models relying solely on magnetic winds.

Findings

Viscosities with α ≥ 10^{-4} explain observed accretion rates.

Models with low viscosity align better with the minimum mass solar nebula.

Hydrodynamic turbulence offers a plausible mechanism for disc accretion.

Abstract

We conjecture that observed protoplanetary disc accretion rates may be explained with low viscosities which could be the result of hydrodynamic turbulence. We show that viscosities parameterized in the usual way with $\alpha \gtrsim 10^{-4}$, comparable to values suggested for hydrodynamic turbulence, can explain the observed accretion rates and lifetimes with plausible inner disc surface densities. Our models are also in better agreement with surface density estimates of the minimum mass solar nebula than models with rapid transport for a given mass accretion rate, such as recent models of accretion driven by magnetic winds. The required surface densities are a natural result of the protostellar infall phase, as long as non-gravitational transport is limited. We argue that, in addition to possible non-ideal magnetic transport due to disc winds possibly modified by the Hall effect, the effects of low-viscosity hydrodynamic accretion deserve more consideration.