A planetary nebula is an expanding, glowing shell of ionized gas that is ejected from a dying star of intermediate mass (about 1 to 8 times the mass of the Sun) during the late stages of its life. When such a star exhausts its fuel, it expands into a red giant and then sheds its outer layers into space. The exposed hot core emits ultraviolet radiation that ionizes the expelled gas, causing it to glow and form the nebula
. Despite the name, planetary nebulae have nothing to do with planets. The term originated in the 18th century because early astronomers observed their round, planet-like appearance through telescopes
. These nebulae are relatively short-lived, lasting only about 20,000 to a few tens of thousands of years before dispersing into space
. Planetary nebulae often display complex shapes and vivid colors due to different chemical elements in the gas. They play an important role in enriching the interstellar medium with elements formed inside stars
. The central star eventually becomes a white dwarf after the nebula fades away
. In summary, a planetary nebula is:
- A glowing shell of ionized gas expelled by a dying intermediate-mass star.
- Ionized by ultraviolet radiation from the hot stellar core.
- A transient phase lasting tens of thousands of years.
- Named for its planet-like appearance but unrelated to actual planets.
- Important for recycling stellar material into the galaxy
