What causes the formation of planetary nebulae?

Planetary nebulae are formed by the ejected outer layers of dying low to intermediate mass stars.

When a star exhausts its fuel, it undergoes a series of changes that ultimately lead to its death. For low to intermediate mass stars, the final stage is the formation of a planetary nebula. As the star runs out of fuel, it expands into a red giant and starts to shed its outer layers. These layers are ejected into space, forming a shell around the central core of the star.

The ejected material is ionised by the intense ultraviolet radiation from the hot core, causing it to glow brightly and form a planetary nebula. The shape of the nebula is determined by the interaction between the ejected material and the hot core. The core eventually cools down and becomes a white dwarf, while the planetary nebula continues to expand and disperse into space.

Planetary nebulae are important objects for studying the late stages of stellar evolution. They provide clues about the chemical composition of the universe and the processes that govern the formation and evolution of stars. Studying planetary nebulae can also help us understand the fate of our own Sun, which will eventually go through a similar process and form a planetary nebula billions of years from now.