What critical threshold describes when gravity begins to dominate internal pressure in a collapsing cloud?
Answer
Jeans instability
The stability of an interstellar gas cloud hinges on the contest between gravity pulling material inward and the gas pressure pushing outward. The Jeans instability defines the precise critical condition under which this balance is broken in favor of collapse. If a specific region within the cloud achieves a density threshold, or if external compression—such as a shockwave from a nearby supernova—is applied that significantly increases the local density, gravity will overcome the resistance provided by the internal pressure. Once this threshold is crossed, the collapse accelerates rapidly, leading directly toward the formation of a stellar core.
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