An alternative model for the origin of gaps in circumstellar disks

TL;DR

This paper investigates the formation and properties of gaps in circumstellar disks caused by counter-rotating environments, revealing that such gaps can be long-lived and resemble planet-induced gaps, complicating observational identification.

Contribution

It introduces a model for gap formation in counter-rotating disks due to external replenishment, demonstrating their potential longevity and similarity to planet-induced gaps.

Findings

Counter-rotating disks can form over a wide range of environmental conditions.

Gaps can be long-lived, lasting comparable to disk lifetimes.

Gaps in counter-rotating disks can resemble planet-induced gaps, complicating observations.

Abstract

Motivated by recent observational and numerical studies suggesting that collapsing protostellar cores may be replenished from the local environment, we explore the evolution of protostellar cores submerged in the external counter-rotating environment. These models predict the formation of counter-rotating disks with a deep gap in the gas surface density separating the inner disk (corotating with the star) and the outer counter-rotating disk. The properties of these gaps are compared to those of planet-bearing gaps that form in disks hosting giant planets. We employ numerical hydrodynamics simulations of collapsing cores that are replenished from the local counter-rotating environment, as well as numerical hydrodynamic simulations of isolated disks hosting giant planets, to derive the properties of the gaps that form in both cases. Our numerical simulations demonstrate that counter-rotating disks can form for a wide range of mass and angular momentum available in the local environment. The gap that separates both disks has a depletion factor smaller than 1%, can be located at a distance from ten to over a hundred AU from the star, and can propagate inward with velocity ranging from 1 AU/Myr to >100 AU/Myr. Unlike our previous conclusion, the gap can therefore be a long-lived phenomenon, comparable in some cases to the lifetime of the disk itself. For a proper choice of the planetary mass, the viscous \alpha-parameter and the disk mass, the planet-bearing gaps and the gaps in counter-rotating disks may show a remarkable similarity in the gas density profile and depletion factor, which may complicate their observational differentiation.