Found in space: Complex carbon-based molecules

March 19, 2021

(Nanowerk News) Much of the carbon in space is believed to be in the form of large molecules called polycyclic aromatic hydrocarbons (PAHs). Since the 1980s, situational evidence has shown that these molecules are abundant in space, but have not been directly observed.

Now, a team of researchers led by MIT Assistant Professor Brett McGuire has identified two unique PAHs in a place called the Taurus Molecular Cloud (TMC-1). It was believed that PAHs would effectively form only at high temperatures ?? on Earth, they occur as byproducts of burning fossil fuels, and are also found in car traces of grilled food. But the interspecific cloud where the research team observed them has not started to form stars, and the temperature is around 10 degrees above absolute zero.

This finding suggests that these molecules may form at much lower temperatures than expected, and may lead scientists to reconsider their assumptions about space. the chemistry of PAH in the formation of stars and planets, the researchers say.

?? What makes the discovery so important is that not only have we proven a hypothesis that has been 30 years in the making, but now we can take a look at the other molecules in this same source and ask how they react to the PAHs we see, how might the PAHs we see react with other objects to form larger molecules, and what effect might it have on our understanding of the role of very large carbon molecules in the formation of planets and stars,? ? said McGuire, lead author of the new study.

Michael McCarthy, associate director of the Harvard-Smithsonian Center for Astrophysics, is another senior author of the study, which features in Science (“Detection of two interspecific polycyclic aromatic hydrocarbons by spectral filtration”). The research team also includes scientists from several other institutions, including the University of Virginia, the National Radio Astronomy Observatory, and NASA’s Space Flight Center?

Special features

Beginning in the 1980s, astronomers have used telescopes to detect infrared signals that suggested the presence of aroma molecules, which are molecules that typically consist of one or more carbon rings. It is believed that about 10 to 25 percent of the carbon in space is found in PAHs, which contain at least two carbon rings, but the infrared signals were not specific enough to identify specific molecules.

That means we cannot dig into the exact chemical mechanisms for how these are formed, how they react with each other or with other molecules, how they destroy them, and the full cycle of carbon during the creation process. stars and planets and finally life, ?? McGuire says.

Although radio astronomy has been a workflow of molecular detection in space since the 1960s, radio telescopes have only been powerful enough to detect these giant molecules for just over a decade. Can these telescopes pick up molecules ?? rotating spectra, which are special patterns of light that molecules emit as they move through space. Researchers can then try to match patterns observed in space with patterns they have seen from these same molecules in laboratories on Earth.

?? As soon as you match a pattern, you know that there are no other molecules that can provide that exact spectrum. And, the intensity of the lines and the relative strength of the different parts of the pattern tell you something about how many molecules there are, and how warm or cold the molecule is, ?? McGuire says.

McGuire and his colleagues have been studying TMC-1 for several years because previous observations have revealed that it is rich in complex carbon molecules. A few years ago, one member of the research team saw suggestions that benzonitrile is in the cloud ?? a six-carbon ring attached to a nitrile (carbon-nitrogen) group.

The researchers then used the Green Bank Telescope, the largest steerable radio telescope in the world, to determine the presence of benzonitrile. In their data, they also found signatures of two other molecules ?? the PAHs reported in this study. These molecules, called 1-cyanonaphthalene and 2-cyanonaphthalene, consist of two benzene rings bonded together, with a nitrile group attached to one ring.

?? The discovery of these molecules is a major step forward in astronomy. We are starting to connect the dots between small molecules ?? mar benzonitrile ?? which has been known in space, to the monolithic PAHs that are so important in astronauts, ?? said Kelvin Lee, an MIT postdoc who is one of the study’s authors.

Detection of these molecules in the cold, without star TMC-1, reveals that PAHs are not just products from dying stars, but may be collection from smaller molecules.

?? In the place where we found them, there is no star, so either they build them in their place or they are the rest of a dead star, ?? McGuire says. ?? We think maybe a combination of the two ?? the evidence shows that it is not one path or the other. That’s new and interesting because there was no speculative evidence for this path from the bottom up. ??

Carbon chemistry

Carbon plays a vital role in the formation of planets, so the suggestion that PAH may be present even in cold, unstarred areas may inspire scientists to rethink it. their theories about the chemicals available during planet formation, McGuire says. As PAHs react to other molecules, they may begin to form interspecific dust grains, which are the seeds of asteroids and planets.

?? We need to completely rethink our models of how the chemistry is evolving, starting from these unstarred coriander, to assume that they form the molecules. great aroma that, ?? he says.

McGuire and his colleagues now plan to further explore how these PAHs were created, and what kinds of reactions they might have in space. They also plan to continue scanning TMC-1 with the powerful Green Bank Telescope. Once they get these observations from the interspecific cloud, the researchers can try to match the names they find with data they generate on Earth by placing two molecules in reactor and explode them with kilovolts of electricity, breaking them into pieces and allowing them to propagate. This could lead to hundreds of different molecules, many of which have never been seen on Earth.

?? We need to continue to see what molecules are present in this interspecific source, because the more we know about the inventory, the more we can start experimenting with the pieces of the web link this link, ?? McGuire says.