planetary nebula

American  

noun

Astronomy.

1. an expanding shell of thin ionized gas that is ejected from and surrounds a hot, dying star of about the same mass as the sun; the gas absorbs ultraviolet radiation from the central star and reemits it as visible light by the process of fluorescence.

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planetary nebula British  

noun

1. 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

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planetary nebula Scientific  

/ plăn′ĭ-tĕr′ē /

1. 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.

2. See more at white dwarf

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Etymology

Origin of planetary nebula

First recorded in 1850–55; so named for its resemblance to the planets Uranus and Neptune

Example Sentences

These sources include pulsars, planetary nebulae, compact HII regions -- which are dense, ionized gas clouds in space -- as well as distant galaxies that lie far beyond the Milky Way.

From Science Daily

Multiple theories were proposed to explain the origin of ORCs, including planetary nebulae and black hole mergers, but radio data alone could not discriminate between the theories.

From Science Daily

Astronomers think that the structure is unique to ageing red-giant stars that will soon end to become planetary nebulae.

From Space Scoop

The so-called "planetary nebulae" is a misnomer that dates back to the 18th century, when the astronomer William Herschel mistook their curved shapes for those of planets.

From BBC

The colorful cloud in the image—somewhat misleadingly called a planetary nebula—is only a few thousand years old.

From Scientific American