What external cosmic event is mentioned as an effective trigger for initiating gravitational collapse in a quiescent cloud?

Answer

Supernova explosion

The shockwave generated by a supernova explosion blasts gas into space, slamming into a quiescent molecular cloud, compressing sections dramatically, and creating localized high-density regions where gravity can take control.

What external cosmic event is mentioned as an effective trigger for initiating gravitational collapse in a quiescent cloud?
astronomygravitynebulastar formation