The distribution of accretion rates as a diagnostic of protoplanetary disc evolution

TL;DR

This paper demonstrates that analyzing the distribution of accretion rates in protoplanetary discs can distinguish between viscous and wind-driven accretion mechanisms, guiding future observational strategies.

Contribution

It shows that a large, homogeneous sample of accretion rates can differentiate accretion models, addressing a key question in disc evolution.

Findings

Current data are insufficient to distinguish models.

Homogeneous surveys can identify the dominant accretion mechanism.

Viscous accretion implies low photoevaporation rates.

Abstract

We show that the distribution of observed accretion rates is a powerful diagnostic of protoplanetary disc physics. Accretion due to turbulent ("viscous") transport of angular momentum results in a fundamentally different distribution of accretion rates than accretion driven by magnetised disc winds. We find that a homogeneous sample of $\gtrsim$300 observed accretion rates would be sufficient to distinguish between these two mechanisms of disc accretion at high confidence, even for pessimistic assumptions. Current samples of T Tauri star accretion rates are not this large, and also suffer from significant inhomogeneity, so both viscous and wind-driven models are broadly consistent with the existing observations. If accretion is viscous, the observed accretion rates require low rates of disc photoevaporation ($\lesssim$$10^{-9}$M$_{\odot}$yr$^{-1}$). Uniform, homogeneous surveys of stellar accretion rates can therefore provide a clear answer to the long-standing question of how protoplanetary discs accrete.