Planetary nebulae
A planetary nebula is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. Despite their name, they are unrelated to planets; the term originated from their planet-like appearance through early telescopes.
Planetary nebulae form at the end of intermediate-mass stars, about 1-8 solar masses. They are relatively short-lived phenomena, lasting perhaps a few tens of millennia. When the star's hot core is exposed, ultraviolet radiation ionizes the ejected gas, making it glow. These nebulae matter because they play a crucial role in the chemical evolution of galaxies by expelling elements created in stars into the interstellar medium, enriching space with carbon, oxygen, and other heavy elements.
Sources
- en.wikipedia.org: “A planetary nebula is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives.”
- en.wikipedia.org: “All planetary nebulae form at the end of the life of a star of intermediate mass, about 1-8 solar masses.”
- en.wikipedia.org: “They are relatively short-lived phenomena, lasting perhaps a few tens of millennia, compared to considerably longer phases of stellar evolution.”
- en.wikipedia.org: “Planetary nebulae probably play a crucial role in the chemical evolution of the Milky Way by expelling elements into the interstellar medium from stars where those elements were created.”