A Star Cluster in Motion . ... Credit Copyright: Adam Block ( NOAO ) Explanation: Star clusters are a swarm of complex motions. The stars that compose globular clusters and many open clusters all orbit the cluster center, occasionally interacting, gravitationally, with a close-passing star. ... Cluster stars frequently fall more directly toward the center and many times trace out unusual and complex loops . The vast space inside a cluster result in stars colliding only rarely. ...