Page "Open cluster" Paragraph 13

Many factors may disrupt the equilibrium of a giant molecular cloud, triggering a collapse and initiating the burst of star formation that can result in an open cluster.

These include shock waves from a nearby supernova, collisions with other clouds, or gravitational interactions.

Even without external triggers, regions of the cloud can reach conditions where they become unstable against collapse.

The collapsing cloud region will undergo hierarchical fragmentation into ever smaller clumps, including a particularly dense form known as infrared dark clouds, eventually leading to the formation of up to several thousand stars.

This star formation begins enshrouded in the collapsing cloud, blocking the protostars from sight but allowing infrared observation.

In the Milky Way galaxy, the formation rate of open clusters is estimated to be one every few thousand years.