Vol. 577
In section 6. Interstellar and circumstellar matter

Top-down formation of fullerenes in the interstellar medium

by O. Berné, J. Montillaud, and C. Joblin, A&A 577, A133


It is fairly well established now that Buckminsterfullerene, or C60, is present in both reflection nebulae and circumstellar shells. Polycyclic aromatic hydrocarbons (PAHs) with probably 50-100 C atoms are also found in such regions, and it is natural to think that there is a connection between the two. Could one be made from the other? Berné and collaborators study the particular example of the possible transformation of a PAH C66H20 into C60. They conclude that, as depicted in the figure, this must first involve dehydrogenation, followed by a folding process and finally shrinkage (with loss of C2 units) to the familiar football-like shape of fullerene. They find that for the conditions of the reflection nebula NGC 7023, this could reasonably take place in about 10^5 years, which seems reasonable. The amount of fullerene formed seems also consistent with that observed, and thus this is the outline of a model that can be tested with more detailed studies.