What atomic process causes the nebula to actually produce visible light after ionization has occurred?

Answer

Recombination

The visible light is generated during recombination, where free electrons are recaptured by hydrogen nuclei, cascade down energy levels, and release discrete packets of light (photons).

What atomic process causes the nebula to actually produce visible light after ionization has occurred?

#Videos

How Does Ionization Cause Emission Nebulae To Glow? - YouTube

What Makes An Emission Nebula (HII Region) Glow? - YouTube

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