We compare the observed size distribution of circum stellar disks in the Orion Trapezium cluster with the results of N -body simulations in which we incorporated an heuristic prescription for the evolution of these disks .
In our simulations , the sizes of stellar disks are affected by close encounters with other stars ( with disks ) .
We find that the observed distribution of disk sizes in the Orion Trapezium cluster is excellently reproduced by truncation due to dynamical encounters alone .
The observed distribution appears to be a sensitive measure of the past dynamical history of the cluster , and therewith on the conditions of the cluster at birth .
The best comparison between the observed disk size distribution and the simulated distribution is realized with a cluster of N = 2500 \pm 500 stars with a half-mass radius of about 0.5 pc in virial equilibrium ( with a virial ratio of Q = 0.5 , or somewhat colder Q \simeq 0.3 ) , and with a density structure according to a fractal dimension of F \simeq 1.6 .
Simulations with these parameters reproduce the observed distribution of circum stellar disks in about 0.2–0.5 Myr .