The 3D structure of disc-instability protoplanets

Abstract

Context. The model of disc fragmentation due to gravitational instabilities offers an alternate formation mechanism for gas giant planets, especially those on wide orbits. Aims. Our goal is to determine the 3D structure of disc-instability protoplanets and to examine how this relates to the thermal physics of the fragmentation process. Methods. We modelled the fragmentation of gravitationally unstable discs using the SPH code PHANTOM, and followed the evolution of the protoplanets formed through the first and second-hydrostatic core phases (up to densities 10−3 g cm−3). Results. We find that the 3D structure of disc-instability protoplanets is affected by the disc environment and the formation history of each protoplanet (e.g. interactions with spiral arms, mergers). The large majority of the protoplanets that form in the simulations are oblate spheroids rather than spherical, and they accrete faster from their poles. Conclusions. The 3D structure of disc-instability protoplanets is expected to affect their observed properties and should be taken into account when interpreting observations of protoplanets embedded in their parent discs.