Disk-fed giant planet formation

TL;DR

This paper proposes that the entropy of material accreted by giant planets during formation is governed by boundary layer processes, significantly influencing their evolution and observable properties like luminosity and radius.

Contribution

It introduces a model emphasizing boundary layer effects in circumplanetary accretion, challenging traditional cold/hot start assumptions in giant planet formation.

Findings

Boundary layer scale-height determines planet's evolutionary track.

Wide range of luminosity and radius outcomes based on accretion details.

Understanding young giant planets requires detailed circumplanetary accretion models.

Abstract

Massive giant planets, such as the ones being discovered by direct imaging surveys, likely experience the majority of their growth through a circumplanetary disc. We argue that the entropy of accreted material is determined by boundary layer processes, unlike the "cold-" or "hot-start" hypotheses usually invoked in the core accretion and direct collapse scenarios. A simple planetary evolution model illustrates how a wide range of radius and luminosity tracks become possible, depending on details of the accretion process. Specifically, the proto-planet evolves towards "hot-start" tracks if the scale-height of the boundary layer is $\gtrsim0.24$, a value not much larger than the scale-height of the circumplanetary disc. Understanding the luminosity and radii of young giant planets will thus require detailed models of circumplanetary accretion.