The collapse of protoplanetary clumps formed through disc instability: 3D simulations of the pre-dissociation phase

TL;DR

This paper uses 3D simulations to study the collapse of protoplanetary clumps formed by disc instability, revealing rapid collapse timescales and the potential for clumps to survive migration and form gas giants.

Contribution

It provides a detailed 3D simulation analysis of clump collapse, including effects of rotation, asymmetries, and cooling, advancing understanding beyond previous 1D models.

Findings

Collapse occurs faster than some previous models predicted.

Rotation leads to circumplanetary disc formation and angular momentum transport.

Clumps may survive migration and form gas giants at a few AU.

Abstract

We present 3D smoothed particle hydrodynamics simulations of the collapse of clumps formed through gravitational instability in the outer part of a protoplanetary disc. The initial conditions are taken directly from a global disc simulation, and a realistic equation of state is used to follow the clumps as they contract over several orders of magnitude in density, approaching the molecular hydrogen dissociation stage. The effects of clump rotation, asymmetries, and radiative cooling are studied. Rotation provides support against fast collapse, but non-axisymmetric modes develop and efficiently transport angular momentum outward, forming a circumplanetary disc. This transport helps the clump reach the dynamical collapse phase, resulting from molecular hydrogen dissociation, on a thousand-year timescale, which is smaller than timescales predicted by some previous spherical 1D collapse models. Extrapolation to the threshold of the runaway hydrogen dissociation indicates that the collapse timescales can be shorter than inward migration timescales, suggesting that clumps could survive tidal disruption and deliver a proto-gas giant to distances of even a few AU from the central star.