What is a planetary nebula?

A planetary nebula is indeed a stage in the life of a low mass star. This phase occurs after a star has exhausted the nuclear fuel in its core and has begun to shed its outer layers. As the star runs out of hydrogen to fuse into helium, it expands into a red giant and ultimately ejects its outer envelope, creating a glowing shell of ionized gas. The central remnant of the star, typically a white dwarf, emits intense ultraviolet radiation that ionizes the expelled gas, causing it to shine brightly.

In the context of stellar evolution, this stage is crucial for enriching the surrounding interstellar medium with heavier elements produced during the star’s lifetime, contributing to the formation of new stars and planets. It’s important to note that this phenomenon is distinct from the settings described by the other choices, which pertain to galaxies and supernova events that involve different processes and mass ranges.