What caused the nebula to collapse?

A nebula typically collapses due to gravitational forces overcoming internal pressure. This can be triggered by various events, such as a nearby supernova explosion, which sends shockwaves through the gas and dust, or the accumulation of mass within the nebula itself. As the material becomes denser, gravity pulls more matter together, leading to the formation of stars and other celestial bodies. Ultimately, this process is part of the cycle of star formation in the universe.