What observation confirms that spiral arm structures are areas of active stellar birth?

Answer

Younger, brighter objects concentrate along the traced arm segments.

Studies involving visible star clusters and molecular clouds show that the newest and brightest stellar components are found concentrated along the segments traced by the hydrogen mapping.

What observation confirms that spiral arm structures are areas of active stellar birth?

#Videos

We Can't Explain Spiral Galaxies - The Winding Problem - YouTube

Which Spiral Arm Of The Galaxy Is Ours? - YouTube

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