In dark, cold clouds of interstellar gas, astronomers have for several years been spotting aromatic molecules — compounds built around a benzene ring (a hexagon of carbon atoms), like the benzene we know. One such substance, benzonitrile (benzene with a cyano group attached), had only been found in very calm and cold places, like the Taurus cloud. Chemical models predicted that in hotter, more turbulent regions it should be far less abundant. New observations turn that idea on its head: benzonitrile has been found in the very heart of the Milky Way, where gas is heated, churned by shock waves, and bathed in harsh radiation.
Using the 40-meter Yebes radio telescope in Spain, astronomers conducted an ultra-deep survey of two clouds in the Central Molecular Zone of the Galaxy — G+0.693-0.027 and G+0.633-0.0604. They captured the faint emission of benzonitrile at frequencies of 31–50 GHz and measured the number of molecules. It turned out to be nearly the same as in cold clouds: roughly 4–6 molecules per 100 billion hydrogen molecules. That's a tiny trace. But its consistency across different conditions suggests that aromatic compounds are hardy and widespread residents of the interstellar medium.
Such resilience of aromatic molecules in harsh conditions forces a fresh look at the carbon cycle in space. If benzene rings don't break down under heat and shocks, they can accumulate and make up a significant part of interstellar dust and gas. It's like how embers remain in a campfire after everything else has burned away: aromatic structures turn out to be the last to hold on in the fire.
Benzonitrile is a close cousin of benzene, which we know by its smell at gas stations, but in space it doesn't smell: it's detected by the radio waves emitted by the rotating molecule.