What causes the ejected shell of gas to become visible as a planetary nebula?
Answer
Intense ultraviolet radiation from the hot core ionizes the expanding gas cloud
The newly revealed white dwarf core becomes incredibly hot, emitting copious amounts of high-energy ultraviolet radiation. This UV light strips electrons from the previously ejected gas—a process called ionization—and when electrons are recaptured, the gas emits light in vibrant colors.
#Videos
How Does A Red Giant Become A Planetary Nebula? - YouTube
How Do Red Giants Create Planetary Nebulae? - Physics Frontier
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