PerspectiveAstronomy

Fullerenes and Cosmic Carbon

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Science  03 Sep 2010:
Vol. 329, Issue 5996, pp. 1159-1160
DOI: 10.1126/science.1194855

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Summary

Carbon is formed by fusion reactions in the cores of stars, and in the late stages of stellar evolution, massive stellar winds expel it into interstellar space. Atomic carbon participates in gas and solid-state chemical reactions to form a variety of organic compounds within circumstellar regions and interstellar clouds (1). Spectroscopic studies of these regions have long provided tantalizing clues to the presence of large carbon molecules that contain many aromatic rings. Candidate molecules include polycyclic aromatic hydrocarbons (PAHs), in which the rings join in flat sheets, and fullerenes, in which they form closed cages. New spectroscopic observational and analytical tools are helping to pin down which molecules are present, as well as characterize the environments that lead to their formation. On page 1180 of this issue, Cami et al. (2) report the detection, by means of the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope, of vibrational bands of the fullerenes C60 and C70 as neutral molecules, likely attached to dust grains, in the young planetary nebula Tc 1. There was no evidence of other major carbon compounds, such as PAHs, in this hydrogen-poor environment. These observations raise important questions about the formation and evolution of fullerene compounds in circumstellar regions.