Evolution of carbon particles from the stage of asymptotic giant branch stars to planetary nebulae: observations, experiments, and theory

We review research into the evolution of carbon particles at stages from the envelopes of asymptotic giant branch stars to planetary nebulae. The evolution of carbon particles is discussed from several standpoints: observational data are summarized; the formation mechanisms and clustering of aromatic molecules are considered; conditions for the formation of carbon particles in the envelopes of stars and for their subsequent evolution in protoplanetary and planetary nebulae are described; results of experiments on creating equivalents of interstellar dust and analyzing their characteristics are presented; and, finally, possible evolutionary scenarios for carbon particles are presented. Particular attention is paid to fullerene molecules, which are important for constructing a comprehensive picture of the evolution. Their presence and nonuniform distribution suggest that, depending on the conditions, the formation of carbon particles can follow two paths: via planar or nonplanar aromatic molecules.