What external event can initiate the large-scale gravitational collapse of a molecular cloud region?

Answer

Shockwave from a nearby supernova explosion

The initial contraction usually requires an external catalyst, such as a shockwave propagating outward from a supernova, to compress a section of the cloud past a critical density.

What external event can initiate the large-scale gravitational collapse of a molecular cloud region?
sequencestarnebulaformation