A team of researchers led by MIT has discovered a significant amount of pyrene, a large carbon-rich molecule known as a polycyclic aromatic hydrocarbon (PAH), within a distant interstellar cloud.
This finding provides new insights into the origins of carbon in our solar system and supports theories about the molecular building blocks that contributed to its formation.
Interstellar clouds and solar system origins
The interstellar cloud in question, known as TMC-1, contains a mix of dust and gas similar to what eventually formed our own solar system. Pyrene’s discovery in this environment suggests it may have played a crucial role in seeding our solar system with carbon.
This idea is further supported by recent findings that pyrene is abundant in samples from the near-Earth asteroid Ryugu, returned by Japan’s Hayabusa2 mission.
“One of the big questions in star and planet formation is: How much of the chemical inventory from that early molecular cloud is inherited and forms the base components of the solar system?” said senior author Brett McGuire, an assistant professor of chemistry at MIT.
“What we’re looking at is the start and the end, and they’re showing the same thing. That’s pretty strong evidence that this material from the early molecular cloud finds its way into the ice, dust, and rocky bodies that make up our solar system.”
Detecting pyrene with radio astronomy
Detecting pyrene in space is a complex process, as its symmetrical structure makes it invisible to conventional radio astronomy methods. To overcome this, the researchers focused on an isomer called cyanopyrene, a version of pyrene modified by cyanide.
This alteration breaks the molecule’s symmetry, allowing it to be detected through its unique rotational spectra – patterns of light emitted as the molecule rotates in space.
The team used the 100-meter Green Bank Telescope (GBT) in West Virginia to identify these signals within TMC-1. This discovery builds on earlier work by McGuire and others, who had identified smaller PAHs in the same region, such as benzonitrile and cyanonaphthalene.
A massive carbon sink in space
The researchers found that cyanopyrene accounts for approximately 0.1 percent of all the carbon present in TMC-1.
McGuire noted that while 0.1 percent doesn’t sound like a large number, most carbon is trapped in carbon monoxide (CO), the second-most abundant molecule in the universe besides molecular hydrogen.
“If we set CO aside, one in every few hundred or so remaining carbon atoms is in pyrene. Imagine the thousands of different molecules that are out there, nearly all of them with many different carbon atoms in them, and one in a few hundred is in pyrene,” said McGuire.
“That is an absolutely massive abundance. An almost unbelievable sink of carbon. It’s an interstellar island of stability.”
The detection of pyrene marks the discovery of the third-largest molecule found in space and the largest yet identified using radio astronomy techniques.
Implications for star and planet formation
Interstellar clouds like TMC-1 have the potential to birth stars and planetary systems as clumps of dust and gas come together, forming new celestial bodies.
The presence of pyrene in TMC-1 and similar molecules in the Ryugu asteroid suggests that such carbon-rich compounds might be directly inherited by forming planetary systems, including our own.
“We now have, I would venture to say, the strongest evidence ever of this direct molecular inheritance from the cold cloud all the way through to the actual rocks in the solar system,” McGuire explained.
The study’s findings have drawn attention from the broader scientific community. Ewine van Dishoeck, a professor of molecular astrophysics at Leiden Observatory in the Netherlands, highlighted the importance of the discovery.
“It builds on their earlier discoveries of smaller aromatic molecules, but to make the jump now to the pyrene family is huge,” said van Dishoeck.
“Not only does it demonstrate that a significant fraction of carbon is locked up in these molecules, but it also points to different formation routes of aromatics than have been considered so far.”
Probing the origins of pyrene
The research team now aims to explore whether even larger PAH molecules exist within TMC-1, providing further insights into the early chemical processes that shape star systems.
The experts are also investigating whether pyrene formed within TMC-1 itself or originated elsewhere in the universe, potentially carried across space by high-energy processes like those found near dying stars.
This study not only offers a deeper understanding of carbon’s role in the formation of planetary systems but also opens new avenues for exploring the molecular origins of life in the cosmos.
As scientists continue to probe the mysteries of space, findings like this bring us closer to understanding the chemical connections between distant clouds and the evolution of our own solar system.
The study is published in the journal Science.
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