Vol. 573
In section 6. Interstellar and circumstellar matter

The effect of external environment on the evolution of protostellar disks

The authors study the gravitational collapse of prestellar cores of subsolar mass embedded in a low-density external environment. They find 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 both (i) compact disks (< 200 AU) shrinking in size because of the infall of external matter with low angular momentum and (ii) extended disks forming because of the 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 or very-low-mass companions. In the case of counter-rotating external environment with high angular momentum, counter-rotating inner and outer disks separated by a deep gap at a few tens of AU can be formed. This model may lead to the emergence of a transient stellar system with substellar or very-low-mass components counterrotating with respect to the star.