Context :

Aims : The aim of this work is to understand to what extend gravitational interactions between the stars in high-density young stellar clusters , like the Orion Nebula Cluster ( ONC ) , change the angular momentum in their protoplanetary discs .

Methods : Two types of simulations were combined — N-body simulations of the dynamics of the stars in the ONC , and angular momentum loss results from simulations of star-disc encounters .

Results : It is shown that in a star-disc encounter the angular momentum loss is usually larger than the mass loss , so that the disc remnant has a lower specific angular momentum .
Assuming an age of 1-2 Myr for the ONC , the disc angular momentum in the higher density region of the Trapezium is reduced by 15-20 % on average .
Encounters therefore play an important part in the angular momentum transport in these central regions but are not the dominant process .
More importantly , even in the outer cluster regions the angular momentum loss is on average 3-5 % .
Here it is shown that a 3-5 % loss in angular momentum might be enough to trigger gravitational instabilities even in low-mass discs - a possible prerequisite for the formation of planetary systems .

Conclusions :