Discovery of seven-ring cyanocoronene in a star-forming cloud challenges assumptions about the abundance and formation of complex organic molecules in the universe
A team of chemists and astronomers have made a groundbreaking discovery in the field of astrochemistry: the identification of cyanocoronene, the largest polycyclic aromatic hydrocarbon (PAH) ever detected in space. This molecule, composed of seven interconnected benzene rings and a cyano group (C₂₄H₁₁CN), was found in the cold, dark molecular cloud TMC-1, a region known for its rich chemistry and as a cradle for new stars.
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.
So how did astronomers discover this massive molecule? The research team first synthesized cyanocoronene in a laboratory and measured its unique microwave spectrum using advanced spectroscopic techniques. Armed with this molecular fingerprint, they searched for cyanocoronene in data from the U.S. National Science Foundation Green Bank Telescope (NSF GBT), the key telescope used in the GOTHAM (GBT Observations of TMC-1: Hunting Aromatic Molecules) project. The research team 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 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.
Scientists are now eager to search for even larger PAHs and their derivatives in space, as well as to further explore how these molecules survive and evolve in the harsh conditions between the stars. Adds Gabi Wenzel, a Research Scientist in the Department of Chemistry at Massachusetts Institute of Technology and the Center for Astrophysics | Harvard & Smithsonian, and lead author on this research, “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.”
This science was shared as part of a press conference at the 246th summer meeting of the American Astronomical Society. Watch a recording from the AAS Press Office here.
About GBO
The Green Bank Observatory, part of the National Radio Astronomy Observatory, is a facility of the U.S. National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.