Polycyclic aromatic hydrocarbons (PAHs) are expected to be the most abundant class of organic molecules in space, yet their their lifecycle in the interstellar medium remains poorly understood. Now, astronomers using NSF’s Green Bank Telescope have detected cyanocoronene (C24H11CN) — the largest PAH ever detected in space — in the starless cloud core TMC-1, which is part of the interstellar Taurus Molecular Cloud.
Cyanocoronene, composed of seven interconnected benzene rings and a cyano group, was found in the cold, dark molecular cloud TMC-1, a region known for its rich chemistry and as a cradle for new stars. Image credit: NSF / AUI / NSF / NRAO / P.Vosteen.
Cyanocoronene is a derivative of coronene, a molecule often described as the prototypical compact PAH due to its stability and unique structure.
PAHs are thought to lock away a significant fraction of the Universe’s carbon and play a key role in the chemistry that leads to the formation of stars and planets.
Until now, only smaller PAHs had been detected in space, with this new discovery significantly pushing the known size limit.
“Each new detection brings us closer to understanding the origins of complex organic chemistry in the Universe — and perhaps, the origins of the building blocks of life themselves,” said Dr. Gabi Wenzel, an astronomer at MIT and the Harvard & Smithsonian’s Center for Astrophysics.
Dr. Wenzel and colleagues first synthesized cyanocoronene in a laboratory and measured its unique microwave spectrum using advanced spectroscopic techniques.
Armed with this molecular fingerprint, the astronomers searched for cyanocoronene in data from the Green Bank Telescope, the key telescope used in the GOTHAM (GBT Observations of TMC-1: Hunting Aromatic Molecules) project.
They detected several distinct spectral lines of cyanocoronene, confirming its presence with a statistical significance of 17.3 sigma — a major detection by astronomical standards.
Cyanocoronene is now the largest individual PAH molecule confirmed in interstellar space, containing 24 carbon atoms in its core structure (excluding the cyano group).
The amount of cyanocoronene found is similar to that of smaller PAHs previously detected, challenging expectations that larger molecules should be rarer in space.
This suggests that even more complex aromatic molecules may be common in the cosmos.
“The presence of such stable, large PAHs supports the idea that these molecules could be a major reservoir of carbon, potentially seeding new planetary systems with the raw materials for life,” the researchers said.
“The study’s quantum chemical approach shows that cyanocoronene can form efficiently in the cold conditions of space through reactions between coronene and the CN radical, with heavily submerged energy barriers that do not slow the process at low temperatures.”
“This means the chemistry that builds complex organics can happen even before stars are born.”
“The discovery of cyanocoronene not only adds a new chapter to the story of cosmic chemistry but also strengthens the PAH hypothesis — the idea that these molecules are responsible for mysterious infrared emission bands seen throughout the Universe.”
“It also draws a direct link between the chemistry of interstellar clouds, meteorites, and asteroids, suggesting that the organic molecules found in our own Solar System may have originated in similar environments long before the Sun formed.”
The scientists presented their findings on June 11 at the AAS246, 246th summer meeting of the American Astronomical Society.
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Gabi Wenzel & GOTHAM Collaboration. 2025. Discovery of the 7-ring PAH Cyanocoronene (C24H11CN) in GOTHAM Observations of TMC-1. AAS246, abstract #75
