Planetary nebula

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The ejected envelope of a dying intermediate-mass star, lit up by the exposed stellar core it surrounds. The name is a historical accident - eighteenth-century observers thought the discs resembled planets - and the objects have nothing to do with planets. The phase is brief: the exposed core must heat past roughly 30,000 K and begin ionising the ejected gas before that gas disperses, and the resulting nebula is visible for something on the order of ten thousand to twenty-five thousand years before fading into the interstellar medium. That is the mechanism by which carbon, nitrogen and other products of intermediate-mass stellar burning are returned to the gas from which the next generation of stars forms. What remains at the centre is a white dwarf. Not a place on Earth.