Star Evolution

What is a planetary nebula?

Planetary nebulae, though their name seems ambiguous, are really clouds of gas. They are called “planetary” because when they were first discovered astronomers saw these nebulae as round and colorful; they looked like the planets in our solar system. A planetary nebula is produced by an intermediate-mass, Sun-like star going through the final stages of its life cycle. As such a star evolves past the red giant stage, the outer gaseous layers detach from the stellar core in a series of violent “puffs,” shedding the atmosphere. Some well-known planetary nebulae include the Ring, the Cat’s Eye, the Hourglass, and the Helix.

The Cat’s Eye Nebula, a type of planetary nebula, is thus called because of its round shape not because it is actually a planet. (NASA, ESA, HEIC, and The Hubble Heritage Team [STScI/AURA])


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