Space & Cosmos

Carbon-storing molecules discovered in distant interstellar clouds may shed light on how our own solar system formed

The Taurus Molecular Cloud, where TMC-1 is located, appears at the top of the image as a dark cloud blocking light from background stars, as seen from Charlottesville, Virginia. Credit: Brett A. McGuire

A team led by MIT researchers has discovered that distant interstellar clouds are rich in pyrene, a type of large carbon-containing molecule known as polycyclic aromatic hydrocarbons (PAHs). .

The discovery of pyrene in this distant cloud resembles the collection of dust and gas that eventually became our solar system, and raises the possibility that pyrene was the source of much of the solar system’s carbon. It suggests that there is. This hypothesis is supported by the recent discovery that samples returned from the near-Earth asteroid Ryugu contain large amounts of pyrene.

“One of the big questions in the formation of stars and planets is how much of the chemistry from the early molecular clouds was inherited and forms the basic building blocks of the solar system. There is a beginning and an end, and they show the same thing, that this material from early molecular clouds is present in the ice, dust, and rocks that make up our solar system. “That’s pretty strong evidence,” says Brett McGuire, assistant professor of chemistry at the university. Massachusetts Institute of Technology.

Pyrene itself is invisible to radio astronomy techniques, which are used to detect about 95% of molecules in the universe, due to its symmetry. Instead, the researchers detected an isomer of cyanopyrene, a version of pyrene that breaks symmetry when it reacts with cyanide. The molecule was detected in a distant cloud known as TMC-1 using the 100-meter Green Bank Telescope (GBT), a radio telescope at the Green Bank Observatory in West Virginia.

McGuire and Ilsa Cook, assistant professor of chemistry at the University of British Columbia, are senior authors of the paper published in Science. Gabi Wenzel, an MIT postdoctoral fellow in McGuire’s group, is the study’s lead author.

carbon in space

PAHs are fused rings of carbon atoms and are thought to store 10-25% of the carbon in the universe. More than 40 years ago, scientists began using infrared telescopes to detect signatures thought to belong to the vibrational modes of PAHs in the universe, but this technique does not reveal exactly what types of PAHs are present. could not be done.

“Since the PAH hypothesis was proposed in the 1980s, many have accepted that PAHs exist in the universe and have been found in samples from meteorites, comets, and asteroids, but in reality, infrared spectroscopy “You cannot clearly identify individual PAHs in space using space,” says Wenzel.

In 2018, McGuire and his team reported the discovery of benzonitrile, a six-carbon ring attached to a nitrile (carbon-nitrogen) group, in TMC-1. To make this discovery, they used GBT. GBT can detect molecules in space by their rotational spectra, the unique light patterns they emit as they roll through space. In 2021, his team detected the first individual PAHs in space. It is two isomers of cyanonaphthalene with two rings fused together and a nitrile group attached to one ring.

On Earth, PAHs commonly occur as a byproduct of fossil fuel combustion and are also found in the charred remains of grilled food. The discovery at TMC-1, which is only about 10 Kelvin, suggested that they could form even at very low temperatures.

The fact that PAHs have also been found in meteorites, asteroids, and comets has led many scientists to hypothesize that they are the source of much of the carbon that formed our solar system. In 2023, Japanese researchers discovered large amounts of pyrene and small PAHs containing naphthalene in samples brought back from the asteroid Ryugu during the Hayabusa2 mission.

This discovery motivated McGuire and his colleagues to search for pyrene on TMC-1. Pyrene contains four rings and is larger than any other PAH detected in space. In fact, it is the third largest molecule seen in the universe and the largest molecule ever detected by radio astronomy.

Before looking for these molecules in space, researchers first needed to synthesize cyanopyrene in the lab. The cyano or nitrile group is necessary for the molecule to emit a signal that can be detected by radio telescopes. The synthesis was performed by MIT postdoc Shuo Zhang in MIT chemistry associate professor Alison Wendlandt’s group.

The researchers then analyzed the signals the molecules gave off in the lab. This was exactly the same signal that molecules emit in space.

The researchers used GBT to discover these signatures throughout TMC-1. They also found that cyanopyrene accounts for about 0.1% of the total carbon in clouds. This sounds small, McGuire said, but it’s important considering the thousands of different types of carbon-containing molecules that exist in the universe.

“0.1% may not seem like a big number, but most of the carbon is trapped in carbon monoxide (CO), which is the second most abundant molecule in the universe after molecular hydrogen. CO If we put that aside, the remaining carbon atoms are found in pyrene, almost all of which have many different carbon atoms; “Imagine being in pyrene. It’s an absolutely huge amount. It’s an almost incredible sink of carbon. It’s a stable interstellar island.”

Ewain van Dyschoek, professor of molecular astrophysics at the Leiden Observatory in the Netherlands, called the discovery “unexpected and exciting.”

“This builds on previous findings on smaller aromatic molecules, but jumping to the pyrene family here is a huge deal. We know that a significant portion of the carbon is trapped in these molecules. “Not only do we demonstrate, but we show that the aromatic pathways are different than previously thought,” says Van Disjok, who was not involved in the study.

Plenty of pyrene

Interstellar clouds like TMC-1 can eventually produce stars, as clumps of dust and gas coalesce into larger objects and begin to heat up. Planets, asteroids, and comets form from some of the gas and dust surrounding young stars. Although scientists cannot look back in time to the interstellar cloud that gave rise to our solar system, the discovery of pyrene on TMC-1 and the presence of large amounts of pyrene within the asteroid Ryugu suggest that pyrene suggests that it may have been the origin of the solar system. It is the source of much of the carbon in our solar system.

“We have, dare I say it, the strongest evidence yet for the direct inheritance of this molecule from cold clouds to the actual rocks of our solar system,” McGuire said. .

The researchers now plan to look for even larger PAH molecules within TMC-1. They also want to investigate the question of whether the pyrene found in TMC-1 formed in cold clouds or arrived from elsewhere in the universe, perhaps from a high-energy combustion process surrounding a dying star. That’s what I think.

Further information: Gabi Wenzel et al., Detection of interstellar 1-cyanopyrene: a tetracyclic polyaromatic hydrocarbon, Science (2024). DOI: 10.1126/science.adq6391. www.science.org/doi/10.1126/science.adq6391

Provided by Massachusetts Institute of Technology

This article is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site covering news about MIT research, innovation, and education.

Citation: Discovery of carbon storage molecules in distant interstellar clouds could shed light on how our own solar system formed (October 24, 2024) https://phys.org/news/ Retrieved October 24, 2024 from 2024-10-discovery-carbonmolecule-distant-interstellar.html

This document is subject to copyright. No part may be reproduced without written permission, except in fair dealing for personal study or research purposes. Content is provided for informational purposes only.

Related Articles

Leave a Reply

Your email address will not be published. Required fields are marked *

Back to top button