Accretion bottleneck in protoplanetary discs: the role of the stellar spin

TL;DR

This study reveals that stellar spin significantly influences accretion rates in protoplanetary discs, with faster spins often causing temporary accretion bottlenecks, highlighting the importance of magnetic interactions in star formation.

Contribution

It demonstrates a correlation between stellar rotation periods and accretion rates, linking stellar spin to accretion regimes through magnetospheric models, and explains the broad variability in disc viscosity.

Findings

Shorter stellar periods correlate with lower accretion rates.

The spread in effective viscosity reflects transitions between accretion states.

Stellar spin regulates mass transfer via magnetospheric interactions.

Abstract

We investigate angular momentum transport and accretion properties in a sample of protoplanetary discs with dynamical measurements of stellar masses, disc masses, and scale radii. From these data we infer effective $\alpha$-viscosities, finding a remarkably broad range spanning over three orders of magnitude. This spread correlates with the stellar rotation period: systems with shorter periods exhibit significantly lower accretion rates, suggesting that they are undergoing at least temporary episodes of accretion bottleneck. We interpret this behaviour within the framework of magnetospheric accretion models, where the transition between steady accretion and the propeller regime is set by the relative locations of the co-rotation and magnetospheric radii. Our results indicate that stellar spin is a key parameter in regulating mass transfer from the disc to the star, and provide new evidence that the observed dispersion in $\alpha$ reflects transitions between distinct accretion states rather than differences in global disc properties.