The effect of external environment on the evolution of protostellar disks

¹ University of Vienna, Department of Astrophysics, 1180 Vienna, Austria
e-mail: eduard.vorobiev@univie.ac.at
² Research Institute of Physics, Southern Federal University, Stachki Ave. 194, 344090 Rostov-on-Don, Russia
³ UCO/Lick Observatory, University of California, Santa Cruz CA 95064, USA

Received: 10 July 2014
Accepted: 29 September 2014

Abstract

Aims. Using numerical hydrodynamics simulations, we studied the gravitational collapse of prestellar cores of subsolar mass embedded into a low-density external environment.

Methods. Four models with different magnitude and direction of rotation of the external environment with respect to the central core were studied and compared with an isolated model.

Results. We found that the infall of matter from the external environment can significantly alter the disk properties as compared to those seen in the isolated model. Depending on the magnitude and direction of rotation of the external environment, a variety of disks can form including compact (≤200 AU) ones shrinking in size owing to infall of external matter with low angular momentum, as well as extended disks forming from infall of external matter with high angular momentum. The former are usually stable against gravitational fragmentation, while the latter are prone to fragmentation and formation of stellar systems with substellar/very-low-mass companions. In the case of a counter-rotating external environment, very compact (<5 AU) and short-lived (≲ a few 10⁵ yr) disks can form when infalling material has low angular momentum. The most interesting case is found for the infall of counter-rotating external material with high angular momentum, leading to the formation of counter-rotating inner and outer disks separated by a deep gap at a few tens AU. The gap migrates inward owing to accretion of the inner disk onto the protostar, turns into a central hole, and finally disappears, giving way to the outer strongly gravitationally unstable disk. This model may lead to the emergence of a transient stellar system with planetary/substellar components counter-rotating with respect to that of the star.