planetary nebula

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planetary nebula:

see nebulanebula
[Lat.,=mist], in astronomy, observed manifestation of a collection of highly rarefied gas and dust in interstellar space. Prior to the 1960s this term was also applied to bodies later discovered to be galaxies, e.g.
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planetary nebula

An expanding and usually symmetrical cloud of gas that has been ejected from a dying star. Most are believed to be the ejected envelopes of red giant stars, shed as a result of instabilities late in their evolution. The gas cloud is ionized by the compact hot burnt-out stellar core that remains in the center of the cloud; the cloud is detected by virtue of the resulting light emission. Planetary nebulae are therefore a class of emission nebulae. They are usually ring-shaped or sometimes hourglass-shaped. They are generally less than 50 000 years old, eventually fading and dispersing into the interstellar medium. The name refers to their resemblance to planetary disks rather than pointlike stars under low magnification. They have a large size range: the smallest objects have a starlike appearance on photographs – and are thus called stellar planetaries – but can be identified by the characteristic spectral emission lines. Planetary nebulae occur in isolation and usually lie close to the galactic plane, concentrated toward the galactic center.

A planetary nebula is believed to form as part of the normal evolution of single stars with masses of up to 8 solar masses; the immediately preceding stage is probably a rapid mass loss OH/IR star. Instabilities eject a succession of planetary nebula shells, reducing the mass of the star until the core (the planetary nebula central star) is only about 0.6 solar masses. This degenerate core becomes a white dwarf. The recent discovery of planetary nebulae with close binary stars at the center suggests that some planetaries form as a result of interactions in a double star system. One star has expanded sufficiently to cocoon both in a common envelope, with the two star cores orbiting inside; frictional drag transfers energy from the orbiting stars to the surrounding gas and thus expels the envelope as a planetary nebula.

Although planetary nebulae are less massive and more symmetrical than H II (ionized hydrogen) regions, their optical spectra are similar. There are bright emission lines of oxygen, hydrogen, nitrogen, and other components, the characteristic green of the inner region being due to doubly ionized oxygen and the red of the outer periphery resulting from singly ionized nitrogen and from hydrogen alpha emission. About 1500 planetary nebulae are known in our Galaxy, the Ring nebula in Lyra being a typical example. See also nebula.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

planetary nebula

[′plan·ə‚ter·ē ′neb·yə·lə]
An oval or round nebula of expanding concentric rings of gas associated with a hot central star.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
In one study, led by Dr Isabel Aleman of the University of Leiden, the Netherlands, 11 planetary nebulas were analysed and the molecule was found in just three.
This is a small planetary nebula, but it's bright enough (magnitude 8.1) to see in any telescope, and if you have even a little bit of aperture (say 4 inches or better) it'll be bright enough to trigger color vision.
"We see in this truly unique planetary nebula is what's closer...
A planetary nebula marks the end of 90% of all stars active lives and traces the star's transition from a red giant to a degenerate white dwarf.
The planetary nebula's bipolar structure is evident in the eyepiece even under low power.
( The paper was published online Wednesday in the journal Monthly Notices of the Royal Astronomical Society, under the title "Herschel Planetary Nebula Survey (HerPlaNS): hydrogen recombination laser lines in Mz 3."
Observers with larger telescopes can hunt for the small, ghostly planetary nebula NGC 2438 on the northeast edge of M46.
Planetary nebula Abell 39 in Hercules has to compete for attention with bright globular clusters M13 and M92.
"The data said you could get bright planetary nebulae from low mass stars like the sun, [while] the models said that was not possible, anything less than about twice the mass of the sun would give a planetary nebula too faint to see."
"What seemed like a double lobe, or 'boomerang' shape, from Earth-based optical telescopes, is actually a much broader structure that is expanding rapidly into space." The Boomerang Nebula, located about 5,000 light-years away in the constellation Centaurus, is a relatively young example of an object known as a planetary nebula. Planetary nebulae, contrary to their name, are actually the end-of-life phases of stars like our Sun that have sloughed off their outer layers.
3 ( ANI ): Astronomers have successfully synthesized the distribution of atomic carbon around a planetary nebula NGC 6302 in test observations with the ALMA Band 8 receiver.
Sketched through his 20cm SCT at x75 it appears like a very small unresolved globular cluster: or perhaps, with a bit of imagination, like Herschel's planet Uranus that led him to coin the term 'planetary nebula' so many years ago.