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

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 magnetized disc winds. We find that a homogeneous sample of & GSIM;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 (& LSIM;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.

Automated summary

We find that the distribution of observed accretion rates is a powerful tool to distinguish between two mechanisms of disc accretion, namely turbulent transport of angular momentum and magnetized disc winds. A sample of 300 observed accretion rates would be sufficient to confidently differentiate between the two mechanisms, even with conservative assumptions. Current observations of T Tauri star accretion rates are too small and heterogeneous to provide a clear answer, making both viscous and wind-driven models valid.