Which term describes a large group of stars, drawn together due to gravitational attraction?

The term that describes a large group of stars held together by gravitational attraction is indeed star clusters. Star clusters are collections of stars that are physically close to each other in space and generally form at the same time from the same molecular cloud, hence sharing a common age and composition. They can vary in size and are often categorized into two main types: open clusters, which are loosely bound and contain a few hundred stars, and globular clusters, which are more tightly bound and can contain thousands to millions of stars.

Understanding this concept is fundamental in astronomy as star clusters can provide insights into stellar formation, the evolution of galaxies, and the dynamics of gravitational forces in space. The other options refer to very different astronomical phenomena; for instance, double stars are pairs of stars that orbit around a common center of mass but do not constitute a large group. A parsec is a unit of measurement used in astronomy to describe distances, and neutron stars are incredibly dense remnants of massive stars that have undergone supernova explosions, not collections of stars.