Astronomers Discover New Building Blocks of Complex Organic Matter
The element carbon is a building block for life, both on Earth and potentially elsewhere in the vast reaches of space. There should be a lot of carbon in space, but surprisingly, it's not always easy to find.
While it can be observed in many places, it doesn’t add up to the volume astronomers would expect to see. The discovery of a new, complex molecule (1-cyanopyrene), challenges expectations about where the building blocks for carbon are found and how they evolve.
Astronomers have long understood that certain carbon-rich stars are soot factories that release copious quantities of small molecular sheets of carbon into the interstellar medium. Scientists thought, however, that these types of carbon-rich molecules could neither survive the harsh conditions of interstellar space nor be re-formed there by combustion-like chemistry because the temperature is far too low.
Researchers from the Center for Astrophysics | Harvard & Smithsonian (CfA) helped lead this research. A paper describing these results was published today in the journal 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,” said Bryan Changala of the CfA, a co-author of the Science paper.
The 1-cyanopyrene molecule is made up of multiple fused benzene rings. It belongs to a class of compounds known as Polycyclic Aromatic Hydrocarbons (PAHs), which were previously believed to form only at high temperatures in regions with lots of energy, like the environments surrounding aging stars. On Earth, PAHs are found in burning fossil fuels, and as char marks on grilled food.
Astronomers study PAHs not just to learn about their particular lifecycle, but to learn more about how they interact with and reveal more about the interstellar medium (ISM) and celestial bodies around them. PAHs are believed to be responsible for the unidentified infrared bands observed in many astronomical objects. These bands arise from the infrared fluorescence of PAHs after they absorb ultraviolet (UV) photons from stars. The intensity of these bands reveal PAHs could account for a significant fraction of carbon in the ISM.
However, the newly observed 1-cyanopyrene molecules were found in Taurus Molecular Cloud-1 (TMC-1), a cold interstellar cloud. Located in the Taurus constellation, TMC-1 has not yet begun forming stars, and the temperature is only about 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,” said Gabi Wenzel, a postdoctoral fellow at the Massachusetts Institute of Technology who led the lab work and is the first author on the Science paper.
“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,” said co-author Brett McGuire, an Assistant Professor of Chemistry at MIT and an adjunct astronomer at the National Science Foundation (NSF) National Radio Astronomy Observatory (NRAO).
Astronomers used the NSF Green Bank Telescope, the largest fully steerable radio telescope in the world, to discover 1-cyanopyrene. Every molecule has a unique rotational spectrum, like a fingerprint, which allows for its identification. However, their large size and lack of a permanent dipole moment, can make some PAHs difficult – or even impossible – to detect. The observations of cyanopyrene can provide indirect evidence for the presence of even larger and more complex molecules in future observations.
“Identifying the unique rotational spectrum of 1-cyanopyrene required the work of an interdisciplinary scientific team,” explains co-author Harshal Gupta, NSF Program Director for the Green Bank Observatory and Research Associate at the CfA. “This discovery is a great illustration of synthetic chemists, spectroscopists, astronomers, and modelers working closely and harmoniously.”
This research combined the expertise of astronomy and chemistry with measurements and analysis conducted in the molecular spectroscopy laboratory of Dr. Michael McCarthy at the CfA.
“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."
About the Center for Astrophysics | Harvard & Smithsonian
The Center for Astrophysics | Harvard & Smithsonian is a collaboration between Harvard and the Smithsonian designed to ask—and ultimately answer—humanity's greatest unresolved questions about the nature of the universe. The Center for Astrophysics is headquartered in Cambridge, MA, with research facilities across the U.S. and around the world.
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