Carbon-chain chemistry in the interstellar medium
Kotomi Taniguchi, Prasanta Gorai, Jonathan C. Tan
Abstract
Abstract The presence of carbon-chain molecules in the interstellar medium (ISM) has been known since the early 1970s and $>130$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>></mml:mo> <mml:mn>130</mml:mn> </mml:math> such species have been identified to date, making up $\sim 43$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>∼</mml:mo> <mml:mn>43</mml:mn> </mml:math> % of the total of detected ISM molecules. They are prevalent not only in star-forming regions in our Galaxy but also in other galaxies. These molecules provide important information on physical conditions, gas dynamics, and evolutionary stages of star-forming regions. Larger species of polycyclic aromatic hydrocarbons (PAHs) and fullerenes (C 60 and C 70 ), which may be related to the formation of the carbon-chain molecules, have been detected in circumstellar envelopes around carbon-rich Asymptotic Giant Branch (AGB) stars and planetary nebulae, while PAHs are also known to be a widespread component of the ISM in most galaxies. Recently, two line survey projects toward Taurus Molecular Cloud-1 with large single-dish telescopes have detected many new carbon-chain species, including molecules containing benzene rings. These new findings raise fresh questions about carbon-bearing species in the Universe. This article reviews various aspects of carbon-chain molecules, including observational studies, chemical simulations, quantum calculations, and laboratory experiments, and discusses open questions and how future facilities may answer them.