A recent discovery, involving the detection of a complex molecule known as 1-cyanopyrene, offers new insight into how carbon-rich compounds form and persist in space. This finding redefines expectations of where and how these molecular building blocks of carbon can exist and evolve.
Typically, scientists believe certain carbon-rich stars act as "soot factories," releasing small carbon molecules into space. However, it was assumed these molecules couldn't withstand the extreme conditions of interstellar space or reform due to low temperatures. This new discovery, led in part by researchers from the Center for Astrophysics | Harvard and Smithsonian (CfA), challenges that notion. Their findings were published in *Science*.
"Our detection of 1-cyanopyrene gives us important new information about the chemical origin and fate of carbon -- the single most important element to complex chemistry both on Earth and in space," explained Bryan Changala of the CfA, co-author of the study.
1-cyanopyrene is a molecule containing fused benzene rings and is part of the Polycyclic Aromatic Hydrocarbon (PAH) family. PAHs, previously believed to form only in high-energy environments around aging stars, are common on Earth in burning fossil fuels and charred foods. In space, astronomers study PAHs to understand their life cycles and how they reveal more about interstellar space and its celestial bodies. The infrared bands they emit after absorbing UV light from stars hint at their abundance and a significant role in the carbon makeup of the interstellar medium (ISM).
Unexpectedly, 1-cyanopyrene was detected in the Taurus Molecular Cloud-1 (TMC-1), a cold interstellar cloud situated in the Taurus constellation, where temperatures hover just 10 degrees above absolute zero. "TMC-1 is a natural laboratory for studying these molecules that go on to form the building blocks of stars and planets," stated Gabi Wenzel, an MIT postdoctoral fellow who spearheaded the lab research and is the lead author on the study.
"These are the largest molecules we've found in TMC-1 to date. This discovery pushes the boundaries of our understanding of the complexity of molecules that can exist in interstellar space," noted Brett McGuire, Assistant Professor of Chemistry at MIT and adjunct astronomer at the NSF's NRAO.
The NSF Green Bank Telescope, the largest steerable radio telescope globally, facilitated this discovery. Each molecule has a distinctive rotational spectrum that enables identification, yet PAHs can be difficult to detect due to their size and lack of a permanent dipole moment. Observations of cyanopyrene may indirectly indicate the presence of even larger molecules for future studies.
"Identifying the unique rotational spectrum of 1-cyanopyrene required the work of an interdisciplinary scientific team," explained Harshal Gupta, NSF Program Director for the Green Bank Observatory and CfA Research Associate. "This discovery is a great illustration of synthetic chemists, spectroscopists, astronomers, and modelers working closely and harmoniously."
The research drew on CfA's expertise in both astronomy and chemistry, with detailed measurements in Dr. Michael McCarthy's molecular spectroscopy lab.
"The microwave spectrometers developed at the CfA are unique, world-class instruments specifically designed to measure the precise radio fingerprints of complex molecules like 1-cyanopyrene," said McCarthy. "Predictions from even the most advanced quantum chemical theories are still thousands of times less accurate than what is needed to identify these molecules in space with radio telescopes, so experiments in laboratories like ours are indispensable to these ground-breaking astronomical discoveries."
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