In terms of physical conditions, what does a strong blue-green (oxygen) signal relative to the red (hydrogen) suggest?

Answer

It is likely hotter or closer to the ionizing stars.

A region showing strong blue-green (oxygen) relative to the red (hydrogen) is likely hotter or closer to the central, hottest ionizing stars, as oxygen requires more energetic radiation to excite.

In terms of physical conditions, what does a strong blue-green (oxygen) signal relative to the red (hydrogen) suggest?

#Videos

Why Are Emission Nebulae Different Colors? - Physics Frontier

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