How are star clusters different from stellar associations?

The primary difference between star clusters and stellar associations lies in their gravitational stability and density.

• Gravitational Binding: Star clusters are groups of stars held together by their mutual gravitational attraction in a relatively tight configuration. In contrast, stellar associations are very loose groupings that lack sufficient self-gravitation to remain stable; they are not gravitationally bound and typically disperse into the surrounding space within a few million years.1234
• Density and Size: Associations are much less dense than clusters, often appearing less dense than the surrounding galactic field. They are also significantly larger, typically measuring 100 to 700 light-years in diameter, whereas clusters are more compact.2345
• Age and Composition: Associations consist of very young stars that share a common place and time of origin, often serving as the birthplaces of stars. While clusters can be quite old (such as globular clusters), associations are strictly limited to the plane of the galaxy where active star formation occurs.34

In many cases, one or more small open star clusters may be found near the center of a larger stellar association.45