Page "Star cluster" Paragraph 17

Open clusters usually contain up to a few hundred members, within a region up to about 30 light-years across.

Being much less densely populated than globular clusters, they are much less tightly gravitationally bound, and over time, are disrupted by the gravity of giant molecular clouds and other clusters.

Close encounters between cluster members can also result in the ejection of stars, a process known as ' evaporation '.