What external event is cited as a potential trigger for initiating gravitational collapse in a Giant Molecular Cloud (GMC)?
Answer
Shockwaves from nearby supernova explosions
Star formation commences when the initial balance within a Giant Molecular Cloud (GMC), where internal pressure counteracts immense gravity, is disrupted. For gravity to overcome the existing pressure, an external trigger is often required. The text specifically lists several such initiating events that can compress regions of the GMC sufficiently to cause fragmentation. These include the passage of the cloud through one of the spiral arms of the galaxy, the physical collision of the cloud with another molecular cloud, or most dramatically, being compressed by shockwaves generated by nearby supernova explosions.
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