Molecular clouds collapse when gravity overcomes internal pressure, leading to star formation.
Understanding Molecular Cloud Collapse
Stars are born within vast, cold, and dense regions of space known as molecular clouds. These clouds, primarily composed of hydrogen molecules, require specific conditions to initiate the process of gravitational collapse, which ultimately leads to the formation of protostars.
The Key Factor: Gravity vs. Pressure
The collapse occurs when the inward force of gravity pulling on the cloud's mass exceeds the outward force of internal pressure. This pressure is primarily caused by the cloud's temperature and density.
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Gravity: Gravity is a fundamental force that attracts all matter. In molecular clouds, gravity acts to pull the cloud's material inward, trying to compress it.
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Internal Pressure: The internal pressure within a molecular cloud is generated by the thermal motion of its constituent particles. This pressure acts outward, resisting the force of gravity.
According to the provided reference, the crucial point is: "When the force of gravity pulling in on the cloud is greater than the strength of internal pressure pushing out, the cloud collapses into a protostar."
The Collapse Process: Step-by-Step
- Initial Equilibrium: Molecular clouds are initially in a state of approximate equilibrium, where gravity and internal pressure are roughly balanced.
- Triggering the Imbalance: Some external event, such as a shockwave from a nearby supernova or the collision of two molecular clouds, can compress a region within the cloud, increasing its density.
- Gravity Dominates: As the density increases, the force of gravity intensifies. If the gravity becomes stronger than the internal pressure, the cloud begins to collapse.
- Fragmentation: As the cloud collapses, it can fragment into smaller, denser clumps. Each clump can then continue to collapse independently.
- Protostar Formation: Within each collapsing clump, the material continues to fall inward, eventually forming a hot, dense core called a protostar.
Factors Influencing Collapse
Several factors can influence the collapse of molecular clouds, including:
- Density: Higher density increases the gravitational force.
- Temperature: Lower temperature reduces the internal pressure.
- Magnetic Fields: Magnetic fields can provide additional support against collapse.
- Turbulence: Turbulence can both support and trigger collapse, depending on its characteristics.
Summary Table
| Factor | Effect on Collapse |
|---|---|
| Gravity | Promotes Collapse |
| Internal Pressure | Resists Collapse |
| Density | Higher Density promotes |
| Temperature | Lower Temp promotes |
