Can photoevaporation open gaps in protoplanetary discs?

TL;DR

This study uses 2D radiation hydrodynamical simulations to examine if photoevaporation alone can create and sustain gaps in protoplanetary discs, challenging the idea that it efficiently forms clean cavities.

Contribution

It demonstrates that photoevaporation alone results in partial, persistent gaps that are refilled by viscous inflow, providing a new prescription for disc evolution models.

Findings

Photoevaporation causes partial, stable gaps in discs.

Refilling by viscous inflow prevents complete clearing.

Outer pressure maxima can trap dust, mimicking transition discs.

Abstract

We investigate whether photoevaporation alone can open and sustain gaps in protoplanetary discs by coupling the evolving disc structure with the photoevaporative flow in two dimensional radiation hydrodynamical simulations. Our results show that once a density depression forms, the local mass-loss rate decreases sharply, suppressing further gap deepening. Viscous inflow and radial mass transport along the disc surface act to partially refill the depleted region, preventing complete clearing. The resulting configuration is a persistent, partially depleted zone whose evolution is largely insensitive to the initial disc morphology. This behaviour challenges the standard paradigm that photoevaporation efficiently carves clean inner cavities and directly produces transition discs. However, the pressure maximum at the outer edge of the depression may still trap dust grains, giving rise to transition disc like observational signatures. We also present a first-order prescription to approximate this behaviour in one dimensional disc evolution models, suitable for use in planet formation and population synthesis studies. Although the prescription improves upon static mass-loss treatments, it remains approximate, underscoring the need for further multidimensional simulations and parameter-space exploration to derive robust recipes for global disc and planet population models.