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en.wikipedia.org/wiki/Planetary_nebula

A planetary nebula, often abbreviated as PN or plural PNe, is a kind of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from old  ...

coolcosmos.ipac.caltech.edu/ask/225-What-is-a-planetary-nebula-

A planetary nebula is created when a star blows off its outer layers after it has run out of fuel to burn. These outer layers of gas expand into space, forming a ...

www.space.com/17715-planetary-nebula.html

May 9, 2016 ... In about 5 billion years, when the sun shucks off its outer layers, it will create a beautiful shell of diffuse gas known as a planetary nebula. About ...

www.schoolsobservatory.org.uk/learn/astro/stars/cycle/planetary

A planetary nebula is an expanding, glowing shell of hot gas (plasma) that is cast off towards the end of a low-mass star's life. Despite the name, they have ...

www.britannica.com/topic/planetary-nebula

planetary nebula: Any of a class of bright nebulae that are expanding shells of luminous gas expelled by dying stars. Observed telescopically, they have a ...

www.noao.edu/jacoby

A planetary nebula forms when a star can no longer support itself by fusion reactions in its center. The gravity from the material in the outer part of the star takes ...

www.sciencedaily.com/terms/planetary_nebula.htm

A planetary nebula is an astronomical object consisting of a glowing shell of gas and plasma formed by certain types of stars at the end of their lives. They are in ...

web.williams.edu/Astronomy/research/PN/nebulae/nebulaegallery.php

A planetary nebula is a beautiful object created during the final stages of the life of a star whose birth mass was between 1 and 8 solar masses. The wispy ...

www.cosmotography.com/images/planetary_nebula_formation.html

Peering down into a vast cosmic maelstrom of gas and dust, the central star in this image of NGC 6853, also known as the Dumbbell Nebula, produced this ...