The largest molecules found in space

The largest molecules found so far in space have been detected. Specifically, these are two molecules that consist of 21 atoms each and that have been located in the cold interstellar cloud TMC-1. The discovery raises new routes to understand the chemical complexity of the universe.

The research that led to this discovery was carried out by an international team led by the Higher Scientific Research Council (CSIC) in Spain.

Located in the Taurus constellation, about 500 light-years away, the interstellar cloud TMC-1 (Taurus Molecular Cloud) is one of the closest to observing the formation of stars like the Sun. This new discovery, in which The 40-meter radio telescope of the National Geographic Institute (IGN) at the Yebes Observatory (Guadalajara, Spain) has been used, which represents a further step in understanding the chemical composition of this star-forming region.

Researchers have identified two cyanide compounds (organic molecules containing cyanide groups in their structure) derived from the polycyclic aromatic hydrocarbon (PAH) acenaphthylene (C12H8). PAHs, whose structure is formed by carbon and hydrogen rings, are found naturally in substances such as coal or gasoline. It is considered that these molecules could be one of the pillars on which the extraterrestrial origin of life would be based.

Careful analysis of the derived rotation constants (transitions between the rotational or spin energy levels of these molecules) has allowed scientists to focus on molecules larger than naphthalene (made up of 10 carbon and 8 hydrogen atoms), but smaller than anthracene and phenanthrene (consisting of 14 carbon and 10 hydrogen atoms, respectively, fused into three benzene rings). The procedure they have used, based on detecting all the rotational lines of these molecules, guarantees unequivocal identification with respect to other techniques that use statistical methods.

Artistic representation of molecules found in space. (Image: IFF)

“These results support a scenario in which PAHs grow in cold clouds from fused carbon rings of five and six carbon atoms and not just six, as was believed until now,” highlights José Cernicharo, CSIC researcher in the Institute of Fundamental Physics (IFF), dependent on the CSIC.

Quantum chemistry calculations, the chemical synthesis of these molecules, as well as the spectroscopic study in the laboratory, support the molecular identifications made by this team. “In the spectrum, the molecules seemed to respond at frequencies of molecules with unpaired electrons, which we call radicals, but it was only in appearance, they were only camouflaged, which until now made their detection difficult,” says the IFF researcher.

These conclusions are part of the Quixote project, which aims to unravel the chemical complexity of a cold interstellar cloud, and which has provided the discovery of more than 90 molecular species in the last four years. One of the most notable results of this collaboration has been the discovery, using the standard line-by-line detection method, of a large amount of pure hydrocarbons with very high abundances.

The study is titled “Discovery of two cyano derivatives of acenaphthylene (C12H8) in TMC-1 with the QUIJOTE line survey” and has been published in the academic journal Astronomy & Astrophysics. (Source: CSIC)