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physical object > natural object > celestial body > nebula > H II region > gaseous nebula > expanding emission nebula

expanding emission nebula
subject			fact

expanding emission nebula	has composition enhanced with heavy elements relative to the interstellar medium
	has explosion date
	has progenitor star
	has expansion velocity
	is a kind of gaseous nebula
gaseous nebula	has catalog gaseous nebula catalog
	has synonym emission nebula
nebula	is a part of gas
celestial body	has spectra
physical object	has location or center of gravity
	has angular momentum
	has mass
	has velocity
	has momentum
	has temperature
	has volume
	has extent
	has material

Kinds of expanding emission nebula :

• nova remnant (6 facts) - an expanding emission nebula produced by a nova
• planetary nebula (27 kinds, 145 facts) - A bubble of gas surrounding a hot, dying star. The star is so hot that it makes the planetary nebula glow, which allows astronomers to see it. The star was once the core of a red giant, which ejected its outer atmosphere and created the planetary. A planetary nebula has nothing to do with a planet, but through a small telescope, it looks like a planet's disk, hence the misleading name., An expanding envelope of rarefied ionized gas surrounding a hot white dwarf. The envelope receives ultraviolet radiation from the central star and reemits it as visible light by the process of fluorescence. The planetary nebula stage lasts for less than 50,000 years. During the core contraction that terminates the red-giant stage, the helium-burning shell is ejected at a velocity so high that it becomes separated from the core. Under current theories, a star with a carbon core and a mass greater than 0.6 M_sun (but less than 4 M_sun) will become a planetary nebula and leave behind a white dwarf. Planetary nebulae are now known to occur in stars less than 4 M_sun whose envelope becomes unstable during the hydrogen shell burning stage.
• supernova remnant (7 kinds, 50 facts) (SNR) - The expanding shell of gas ejected at high speed by a supernova explosion, observed as an expanding diffuse gaseous nebula, often with a shell-like structure., A gaseous nebula, the expanding shell ejected by a supernova, and deriving its energy (at least in some cases) from the conversion by the remanent neutron star of its rotational energy into a stream of high-energy particles being continually accelerated in the SNR. About 100 SNRs are known in our Galaxy. Supernova remnants are usually powerful radio sources.

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