Laboratory evidence of slow-cooling for carbon droplets in red-giant atmospheres

Micron-sized presolar carbon spheres condensed before the origin of our solar system, in the atmosphere of asymptotic giant branch stars from carbon atoms dredged up following nucleosynthesis in the stellar interior, have been extracted by dissolution from primitive carbonaceous chondrite meteorites, identified by noble-gas and major-element isotopic analysis, and available to electron microscopists on earth for over two decades Some of these spheres appear to consist of graphite condensed on carbide grains, but others instead show "graphite-onion" rims that surround a spherical-core of unlayeredgraphene i.e. carbon that in diffraction shows graphite (hk0) spacings only. The high spatial-frequency tail of these graphene lines [5] suggests a graphene-sheet coherence width in the 4-nm size range [1], consistent with electron-phase-contrast images of single (sometimes segmented) edge-on sheets