October 29, 2024 by Matt Williams
Carbon is the building block for all life on Earth and accounts for approximately 45–50% of all dry biomass. When bonded with elements like hydrogen, it produces the organic molecules known as hydrocarbons. When bonded with hydrogen, oxygen, nitrogen, and phosphorus, it produces pyrimidines and purines, the very basis for DNA. The carbon cycle, where carbon atoms continually travel from the atmosphere to the Earth and back again, is also integral to maintaining life on Earth over time.
As a result, scientists believe that carbon should be easy to find in space, but this is not always the case. While it has been observed in many places, astronomers have not found it in the volumes they would expect to. However, a new study by an international team of researchers from the Massachusetts Institute of Technology (MIT) and the Harvard-Smithsonian Center for Astrophysics (CfA) has revealed a new type of complex molecule in interstellar space. Known as 1-cyanoprene, this discovery could reveal where the building blocks of life can be found and how they evolve.
The research was led by Gabi Wenzel, a postdoctoral researcher from the Department of Chemistry at MIT. She was joined by researchers from the CfA, the University of British Columbia, the University of Michigan, the University of Worchester, the University of Virginia, the Virginia Military Institute (VMI), the National Science Foundation (NSF), the National Radio Astronomy Observatory (NRAO), and the Astrochemistry Laboratory at NASA’s Goddard Space Flight Center (GSFC). The paper that describes their findings recently appeared in the journal Science.
For their study, the team relied on the NSF Green Bank Telescope (GBT), the most accurate, versatile, and largest fully-steerable radio telescope in the world, located at the Green Bank Observatory in West Virginia. This sophisticated instrument allowed the team to detect the presence of 1-cyanopyrene based on its unique rotational spectrum. 1-cyanoprene is a complex molecule composed of multiple fused benzene rings and belongs to the polycyclic aromatic hydrocarbon (PAHs) class of molecules. On Earth, they are created by burning fossil fuels or other organic materials, like charred meat or burnt bread.
By studying PHAs, astronomers hope to learn more about their lifecycles and how they interact with the ISM and nearby celestial bodies. As co-author Harshal Gupta, the NSF Program Director for the GBO and a Research Associate at the CfA, explained in a recent CfA press release:
“Identifying the unique rotational spectrum of 1-cyanopyrene required the work of an interdisciplinary scientific team. This discovery is a great illustration of synthetic chemists, spectroscopists, astronomers, and modelers working closely and harmoniously.”
This was an impressive feat due to the difficulty (or even impossibility) of detecting these molecules due to their large size and lack of a permanent dipole moment. “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,” added co-author MIT professor Brett McGuire, who is also an adjunct astronomer at the NSF and the NRAO.
Previously, these molecules were believed to form only in high-temperature environments, like the region surrounding older stars. This concurs with what astronomers have known for a long time about certain carbon-rich stars, which produce massive amounts of small molecular sheets of carbon that they then distribute into the interstellar medium (ISM). In addition, previous research has suggested that the infrared fluorescence of PAHs – caused by the absorption of ultraviolet radiation from nearby stars – could be responsible for infrared bands observed in many celestial objects.
The intensity of these bands has led some astronomers to theorize that PAHs could account for a significant fraction of carbon in the ISM. Other astronomers have maintained that these carbon-rich molecules could not survive the harsh conditions of interstellar space because temperates in the ISM are far too low – averaging about 10 K (-263 °C; -442 °F). However, the 1-cyanopyrene molecules Wenzel and her colleagues observed were located in the nearest star-forming region to Earth, the cold interstellar cloud known as Taurus Molecular Cloud-1 (TMC-1).
Since this Nebula has not yet started forming stars, its temperature is the same as that of the ISM. “TMC-1 is a natural laboratory for studying these molecules that go on to form the building blocks of stars and planets,” said Wenzel. These observations suggest that PHAs like 1-cyanopyrene may have a different formation mechanism entirely and/or can survive the harsh environment of space. In the meantime, detecting cyanopyrene can provide indirect evidence of even larger and more complex molecules in future observations.
This research was supported by measurements and analysis conducted by the molecular spectroscopy laboratory of Dr. Michael McCarthy at the CfA. As he indicated:
“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. 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.”
Further Reading: CfA
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