planetary nebula (redirected from Planetary nebulas)

planetary nebula

n.

1. A nebula, such as the Ring Nebula, consisting of a hot, blue-white, central star surrounded by an envelope of expanding gas.

2. A low-mass star in a later stage of its evolution during which the star ejects its outer layers, often in an expanding spherical shell, exposing the hot stellar core.

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planetary nebula

n

(Astronomy & Space / Celestial Objects) an expanding shell of gas surrounding a dying star, formed from matter ejected from the star's outer layers; the gas is ionized by the remaining hot stellar core, emitting light in the process

[named from its (occasional) resemblance to a planetary disc]

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planetary nebula  (pln-tr)

A nebula consisting of a rapidly expanding shell of glowing gas, mostly hydrogen, ejected from a red giant upon its collapse into a white dwarf. Ultraviolet radiation from the hot, luminous white dwarf ionizes the expanding gas and causes it to glow. The nebula disappears once the cooling dwarf can no longer ionize it, and its material eventually returns to the interstellar medium. See more at white dwarf.

Thesaurus

Noun

1.

planetary nebula - a nebula that was once thought to be a star with its planets but is now thought to be a very hot star surrounded by an expanding envelope of ionized gases that emit a fluorescent glow because of intense radiation from the star nebula - an immense cloud of gas (mainly hydrogen) and dust in interstellar space