Can photoevaporation open gaps in protoplanetary discs?

TL;DR

The paper tests whether photoevaporation alone can carve and sustain gaps in protoplanetary discs by coupling disc evolution with a self-consistent wind in 2D radiation-hydrodynamics. Using a two-phase approach—1D viscous evolution to the gap onset, followed by 2D simulations of the wind-disc interaction—the study reveals a self-regulating mechanism: as a gap forms, the local wind weakens and radial mass transport partially refills the region, leading to a persistent, partially depleted zone rather than a fully evacuated cavity. This challenges the notion that photoevaporation alone creates clean inner holes, though a pressure maximum at the gap edge can still trap dust and imitate transition-disc observations. The authors provide a first-order 1D prescription to incorporate this feedback into disc evolution models, but emphasize that multidimensional simulations and broader parameter exploration are essential for robust planet-formation and population-synthesis implications.

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.

Figures (6)

• Figure 1: Surface density evolution in the 1D model S1. The red dotted line shows the initial conditions for the model with an initial depletion (p-g). For the model without an initial depletion (p-ng), the surface density was modified using the solid red line, as described in \ref{['sec:met:pluto']}.
• Figure 2: Gas density and velocity field of model p-g after 50, 1300, and 2600 orbits. Each panel shows a time average over 10 orbits, taken over the intervals [40–50], [1290–1300], and [2590–2600] orbits, respectively. The white dotted lines represent column number density contours for values of (from top to bottom) $10^{19}, 10^{20}, 10^{21}$, and $10^{22}$ cm$^{-2}$. The black dashed lines are density contours for values of (from top to bottom) $10^{-14}, 10^{-14.5}$, and $10^{-15}$ g cm$^{-3}$.
• Figure 3: 1D surface density evolution of model p-g with an initial depletion (black lines) and p-ng without an initial depletion (blue lines). The solid lines represent the surface density in 400 orbit intervals (from 0 at the top to 2400 orbits at the bottom). The dashed line is the surface density at the end of the simulation at 2600 orbits.
• Figure 4: 1D radial wind mass loss profiles after 500, 1500, and 2500 orbits. The blue dotted line is the profile for a primordial disc by Picogna2019. The black solid line represents the mass loss profile measured in the model, smoothed with a Savitzky-Golay-Filter using second-order polynomials. The grey points show the exact measurements. The black dashed portions mean that the mass-loss is negative. The orange solid line represents the 1D surface density, and the red dotted line is our simple approximation as described in \ref{['sub:mlossprof']}
• Figure 5: Surface density evolution of the 2D p-g model without an initial depletion (p-g; black), the corresponding 1D model with the modified mass-loss prescription (red), and the original 1D model with the mass loss profile by Picogna2019 (blue dashed). Lines of the same colour represent different timesteps at intervals of 25 kyr starting at t=0 (top lines).