Scientists have long been mystified by how large, complex organic molecules like hydrocarbons form so abundantly in the near-vacuum of space, especially when their atomic building blocks are sparse and might interact only rarely. New lab studies suggest that a certain type of organic molecule, instead of being assembled from smaller bits, may instead be produced when ultraviolet light blasts apart the carbon-rich veneer on some types of stardust. Polycyclic aromatic hydrocarbons—or PAHs, which often form when carbon-containing materials like wood, coal, and fossil fuels burn incompletely—come in many shapes and sizes, but they all contain three or more rings of carbon atoms; hence the term “polycyclic.” But graphite, the form of carbon found in pencil lead but also found coating the surface of many particles of interstellar dust, is also made of one-atom-thick sheets of carbon atoms arranged into hexagonal rings. In the new study, researchers placed tiny particles of silicon carbide (one represented by the group of tan molecules in this artist’s concept) covered with graphite (hexagonal networks of gray atoms) in a vacuum chamber that duplicated the deep-space conditions surrounding many stars (temperatures between 900 and 1500 kelvins and pressures less than one-billionth that found at Earth’s surface). Then, they bombarded the faux stardust with intense ultraviolet light and bathed it in single hydrogen atoms, which are found in profusion in the environment near stars. Under certain combinations of conditions, large fragments of carbon coating were eroded away  (as depicted in image), the researchers report today in Nature Communications. If the same processes occur in space, they could generate a blend of free-floating PAHs of various sizes, some of them containing a hundred or more carbon atoms. Such a mélange could help explain observations suggesting the presence of PAHs and other organic molecules around distant stars.
ScienceShot: How to Make Organic Chemicals From Stardust