  AIM: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. METHOD: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.
