GOTHAM Investigators discover warehouse full of complex molecules never seen in space

Radio observations of a cold, dense cloud of molecular gas reveal more than a dozen unexpected molecules.

Scientists have discovered a large, previously unknown reservoir of new aromatic material in a cold, dark molecular cloud by first detecting individual polycyclic aromatic hydrocarbon molecules in the interstellar medium, thus beginning to answer a three-decade-old. scientific mystery: how and where are these molecules formed in space?

“We’d always thought that polycyclic aromatic hydrocarbons were formed primarily in the atmosphere of dying stars,” said Brett McGuire, assistant professor of chemistry at the Massachusetts Institute of Technology and project chief researcher for GOTHAM or Green Bank Telescope (GBT). . of TMC-1: Hunting of aromatic molecules. “In this study, we found them in cold, dark clouds where stars had not even begun to form.”

Aromatic molecules and PAHs – short for polycyclic aromatic hydrocarbons – are known among scientists. Aromatic molecules exist in the chemical composition of humans and other animals and are found in food and medicine. PAHs are also pollutants formed by the combustion of many fossil fuels and are even one of the carcinogenic substances formed when vegetables and meat are charred at high temperatures. “Polycyclic aromatic hydrocarbons presumably contain as much as 25 percent of the carbon in the universe,” said McGuire, who is also a research fellow at the Center for Astrophysics. Harvard & Smithsonian (CfA). “For the first time, we have a direct window into their chemistry, which will allow us to study in detail how this massive carbon reservoir responds and evolves through the formation of stars and planets.”

Scientists suspect the presence of PAHs in space since the 1980s, but the new research published in nine articles published over the past seven months is the first definitive proof of their existence in molecular clouds. To locate the elusive molecules, the team focused the 100 m radioactivity GBT on the Taurus Molecular Cloud, or TMC-1 – a large, pre-star cloud of dust and gas located about 450 light-years from Earth is, which will one day collapse. in itself to form stars – and what they found was astounding: not only were the accepted scientific models wrong, but there was also much more going on in TMC-1 than the team could have imagined.

“From decades of previous modeling, we believed we understood the chemistry of molecular clouds fairly well,” said Michael McCarthy, an astrochemist and acting deputy director of CfA. The research team made the exact laboratory measurements that made many of these possible. astronomical traces to be determined with confidence. “What these new astronomical observations show is that these molecules occur not only in molecular clouds, but also in sizes of greater order than standard models predict.”

McGuire added that previous studies have only revealed that there are PAH molecules, but not which specifics. ‘Scientists have been observing the largest signature of these molecules in our galaxy and other galaxies in the infrared for the past thirty years or so, but we could not see what individual molecules the mass consists of. With the addition of radio astronomy, we see individual molecules instead of seeing this large mass that we cannot distinguish. ‘

To their surprise, the team does not discover just one new molecule hiding in TMC-1. Detailed in multiple articles, the team has 1-sionanophthalene, 1-cyanocyclopentadiene, HC11N, 2-sionanophthalene, vinyl cyanoacetylene, 2-cyanocyclopentadiene, benzonitrile, trans- (E) -cyanovinylacetylene, HC4emcyanyl, HC4emcyanC, ‘It’s like going into a boutique store and just looking at the front page without ever knowing there’s a back room. We have been collecting small molecules for 50 years and now we are discovering that there is a back door. “When we opened the door and entered, we found this huge warehouse with molecules and chemicals that we did not expect,” said McGuire. “It kept peeking out just beyond where we had looked before.”

McGuire and other scientists at the GOTHAM project have been “hunting” for molecules in TMC-1 for more than two years, following the initial detection of benzonitrile in McGuire in 2018. The results of the latest observations of the project may have consequences in astrophysics for years to come. . ‘We have come across a whole new set of molecules, unlike what we were able to detect before, and this will completely change our understanding of how these molecules interact with each other. It has downstream effects, ”McGuire said, adding that these molecules eventually become large enough to accumulate in the seeds of interstellar matter. ‘If these molecules become large enough to become the seeds of interstellar matter, it could affect the composition of asteroids, comets and planets, the surfaces on which ice forms and perhaps even the places where planets are forming within star systems. ”

The discovery of new molecules in TMC-1 also has consequences for astrochemistry, and although the team does not yet have all the answers, the consequences here will also last decades. “We went from one-dimensional carbon chemistry, which is very easy to detect, to real organic chemistry in space in the sense that the newly discovered molecules are molecules that a chemist knows and recognizes and can produce on earth,” he said. said. McCarthy. ‘And that’s just the tip of the iceberg. Whether these organic molecules are synthesized there or transported there, it exists, and knowledge alone is a fundamental advance in the field. ‘

Prior to the launch of GOTHAM in 2018, scientists cataloged approximately 200 individual molecules in the catalogs Milky Waytheir interstellar medium. These new discoveries forced the team to, and rightly so, wonder what was there. “The wonderful thing about these observations, of this discovery and of these molecules, is that no one looked or looked hard enough,” McCarthy said. “It makes you wonder what else we’re not looking for.”

This new aromatic chemistry that scientists find is not isolated from TMC-1. In a companion survey to GOTHAM, known as ARKHAM – a rigorous K / Ka Band test for aromatic molecules – benzonitrile was recently found in several additional objects. “Incredibly, we found benzonitrile in every one of the first four objects observed by ARKHAM,” said Andrew Burkhardt, a sub-doctoral fellow at the CfA and a co-principal investigator for GOTHAM. ‘This is important because although GOTHAM shifts the limit of the chemistry we thought was possible in space, it means that the things we learn in TMC-1 about aromatic molecules can be applied to dark clouds everywhere. These dark clouds are the first birthplace of stars and planets. These previously invisible aromatic molecules will therefore also have to be considered at every subsequent step on the way to the creation of stars, planets and solar systems such as our own. ”

Reference: March 18, 2021, Science.

In addition to McGuire, McCarthy and Burkhardt, the following researchers contributed to and led research for this project: Kin Long Kelvin Lee of MIT; Ryan Loomis, Anthony Remijan and Emmanuel Momjian of the National Radio Astronomy Observatory; Christopher N. Shingledecker of Benedictine College; Steven B. Charnley and Martin A. Cordiner of NASA Goddard; Eric Herbst, Eric R. Willis, Ci Xue and Mark Siebert of the University of Virginia; and Sergei Kalenskii of the Lebedev Physical Institute. The project also received research support from the University of Stuttgart, the Max Planck Institute and the Catholic University of America.

Funding: Center for Astrophysics | Harvard & Smithsonian, Massachusetts Institute of Technology, National Radio Astronomy Observatory, Benedictine College, National Aeronautics and Space Administration Goddard Flight Center, University of Virginia, Lebedev Physica