What critical mass must a cloud region exceed to begin gravitational collapse against internal pressure?
Answer
Jeans Mass
The Jeans Mass represents the minimum mass a region within a molecular cloud must attain for the force of gravity to overcome the internal resistance provided primarily by thermal pressure. If the thermal energy (and associated temperature) is too high, the outward pressure gradient will counteract gravity, preventing collapse or leading only to fragmentation into smaller, stable clumps. Only when a region’s mass significantly exceeds its Jeans Mass threshold does gravity achieve dominance over the internal kinetic energy, initiating the gravitational contraction necessary for forming a star or planetary system. This concept is central to determining where and when structure begins to emerge from the primordial gas and dust.
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