On the diversification and dissipation of protoplanetary disks

TL;DR

This paper proposes a model explaining the diversity in protoplanetary disk evolution, linking magnetic truncation, stellar rotation, and X-ray attenuation to disk lifetime, structure, and planet formation outcomes.

Contribution

It introduces a new scenario where evolving inner disk structures attenuate X-ray driven photoevaporation, accounting for observed disk diversity and planetary system architectures.

Findings

Longer disk lifetimes around lower-mass stars explained.

Inner disk winds and gaps influence planet formation pathways.

X-ray attenuation affects disk dissipation and planet trapping.

Abstract

Protoplanetary disk evolution exhibits trends with stellar mass, but also diversity of structure, and lifetime, with implications for planet formation and demographics. We show how varied outcomes can result from evolving structures in the inner disk that attenuate stellar soft X-rays that otherwise drive photoevaporation in the outer disk. The magnetic truncation of the disk around a rapidly rotating T Tauri star is initially exterior to the corotation radius and ``propeller" accretion is accompanied by an inner magnetized wind, shielding the disk from X-rays. Because rotation varies little due to angular momentum exchange with the disk, stellar contraction causes the truncation radius to migrate inside the corotation radius, the inner wind to disappear, and photoevaporation to erode a gap in the disk, accelerating its dissipation. This X-ray attenuation scenario explains the trend of the longer lifetime, reduced structure, and compact size of disks around lower-mass stars. It also explains an observed lower bound and scatter in the distribution of disk accretion rates. Disks that experience early photoevaporation and form gaps can efficiently trap solids at a pressure bump at 1--10 au, triggering giant planet formation, while those with later-forming gaps or indeed no gaps form multiple smaller planets on close-in orbits, a pattern that is consistent with observed exoplanet demographics.