How do the spiral arms of the Milky Way provide an external trigger for gravitational collapse?

Answer

The increased density of matter within the arms gravitationally compresses the clouds as they orbit through them.

The structure of the galaxy itself offers a large-scale mechanism for triggering star formation. Molecular clouds orbit within the galactic disk, and as they pass through the denser regions known as the spiral arms, they encounter a localized increase in the ambient density of matter. This higher density in the arms exerts a gravitational influence on the cloud, causing external gravitational compression. This external nudge effectively pushes marginally stable molecular clouds across their Jeans Mass threshold, initiating gravitational fragmentation and collapse in specific regions that might otherwise have remained stable for extended periods.

How do the spiral arms of the Milky Way provide an external trigger for gravitational collapse?

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What Initiates Molecular Cloud Collapse? - Physics Frontier - YouTube

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