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Composition and origin

Stardust consists of refractory minerals such as silicates, graphite and amorphous carbon. These solids condense as circumstellar dust around evolved stars such as red giants, carbon stars, novae and supernovae. Red giants are the major source of refractory dust grain cores in galaxies. Stardust forms less than 0.1% of the mass of total interstellar solids. It appears to be totally unprocessed since its thermal condensation within stars as refractory crystalline minerals. Silicate particles condense in the atmospheres of cool, oxygen-rich red giants, and carbon grains condense in the atmospheres of cool carbon stars. Several percent of refractory grain cores have condensed within the expanding interiors of supernovae.

Presolar grains

Presolar grains are hard, refractory, high-temperature solids, and silicon carbide, graphite, aluminium oxide and aluminium spinel are prominent among them. They differ greatly from the solids formed at low temperature within the interstellar medium. Stardust condenses within stars by a condensation chemistry quite different from that of the bulk of cosmic dust, which accretes cold onto existing dust in dark molecular clouds. Meteoriticists often call refractory stardust presolar grains, although the grains found within meteorites are only a small fraction of all presolar dust.

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