Assertion: nebula's shell | /r/LocatedNear | the core
Facets:
Source sentences:
text: Planetary nebulae are formed when stars similar to the size of the Sun use up the hydrogen in their core and instead begin fusing hydrogen in an outer shell surrounding the core.
text: Hydrogen is still available outside the core, so hydrogen fusion continues in a shell surrounding the core.
text: Instead the star will begin to fuse hydrogen in a shell surrounding the core causing it to expand to hundreds of times its original size and cooling its surface, becoming what is known as a red giant.
text: Although fusion is no longer taking place in the core, the rise in temperature heats up the shell of hydrogen surrounding the core until it is hot enough to start hydrogen fusion, producing more energy than when it was a main sequence star," the Australia Telescope National Facility says on their website.
text: Surrounding the core are two shells rich in unprocessed hydrogen and helium.