A semi-analytical model of the outer structure of protoplanetary discs formed by the collapse of a rotating molecular cloud

Abstract

Context. Protoplanetary discs are formed due to the fragmentation and collapse of giant molecular cloud cores. The physical properties and structure of a formed disc are of great importance when studying the onset of planet formation processes. Aims. Starting from the isothermal collapse of a rotating Bonnor-Ebert sphere, and assuming the conservation of angular momentum, we look for the structure equations of the newly formed protoplanetary disc. We take into account the possible role of pressure gradient in forming the initial disc structure, and compare our results with those obtained from a Keplerian infall model. Our aim is to obtain initial conditions to numerically study the evolution of the gaseous and solid components of protoplanetary discs. Methods. The structure equations developed for protoplanetary discs have been derived analytically, while these equations have been solved numerically. Results. The surface density profiles of the newly formed protoplanetary discs strongly depend on the initial rotation state of the Bonnor-Ebert sphere. According to our results, for slow rotators, gravitational instabilities can develop in the early phases of disc formation, while for relatively fast rotators, the outermost regions of the resulting discs are gravitationally stable, quite massive and highly sub-Keplerian, allowing rapid dust transport to the inner disc and subsequent planet formation.