Fullerenes in circumstellar and interstellar environments

TL;DR

This paper discusses the detection, abundance, and formation of fullerenes like C60 and C70 in circumstellar and interstellar environments, highlighting their spectral signatures, abundance estimates, and formation hypotheses.

Contribution

It compiles observational evidence of fullerenes in space, analyzes their spectral properties and abundance, and discusses potential formation mechanisms in astrophysical environments.

Findings

Fullerenes are detected in various circumstellar and interstellar sources.

C60 accounts for approximately 0.1%-1.5% of available carbon.

Fullerene excitation may involve thermal processes rather than single-photon heating.

Abstract

We recently identified several emission bands in the Spitzer-IRS spectrum of the unusual planetary nebula Tc 1 with the infrared active vibrational modes of the neutral fullerene species C60 and C70. Since then, the fullerene bands have been detected in a variety of sources representing circumstellar and interstellar environments. Abundance estimates suggest that C60 represents ~0.1%-1.5% of the available carbon in those sources. The observed relative band intensities in various sources are not fully compatible with single-photon heating and fluorescent cooling, and are better reproduced by a thermal distribution at least in some sources. The observational data suggests that fullerenes form in the circumstellar environments of evolved stars, and survive in the interstellar medium. Precisely how they form is still a matter of debate.