What is a planetary nebula?

A planetary nebula is indeed a shell of gas ejected from a dying star, specifically a red giant that has exhausted its nuclear fuel. As these stars reach the end of their life cycles, they undergo processes that lead to the expulsion of their outer layers into space. This ejected material forms a beautiful and often colorful cloud known as a planetary nebula.

The term "planetary nebula" can be misleading, as it has nothing to do with planets. The name originated from the rounded, planet-like appearance of these nebulae as seen through early telescopes. The core that remains after the outer layers are expelled usually becomes a white dwarf, which is the hot, dense remnant of the star. Over time, the gas and dust in the nebula may contribute to the formation of new stars and planets, enriching the interstellar medium with heavier elements synthesized in the original star.

This understanding highlights the role of planetary nebulae in the life cycle of stars and their contribution to the chemical enrichment of the galaxy, setting the stage for future generations of stars and planets.