Interstellar graphitic particles generated by annealing of nanodiamonds and their relation to the 2175 A peak carrier

Abstract

Since the discovery of the 2175 Angstrom absorption bump, this peak has been associated with graphitic particles. Recent development of carbon cluster physics revealed a very robust nanometric carbon structure: onion-like graphitic particle (multishell fullerene). On the basis of laboratory data, we analyze the possible generation of this kind of cluster in interstellar space. In particular, we speculate that tiny nanodiamonds are formed by a chemical vapor disposition (CVD) process in the circumstellar environment and are subsequently thermally annealed to concentrically shelled graphitic particles. These particles have important implications for the UV bump carrier grains, as they would account for observational constraints requiring a narrow shape distribution and also that hydrogen must be involved in the formation mechanism.