GBT Detection Unlocks Exploration of ‘Aromatic’ Interstellar Chemistry

Summary: Astronomers using the Green Bank Telescope have made the first definitive interstellar detection of benzonitrile, an intriguing organic molecule that helps to chemically link simple carbon-based molecules and truly massive ones known as polycyclic aromatic hydrocarbons. This discovery is a vital clue in a 30-year-old mystery: identifying the source of a faint infrared glow that permeates the Milky Way and other galaxies.

Astronomers had a mystery on their hands. No matter where they looked, from inside the Milky Way to distant galaxies, they observed a puzzling glow of infrared light. This faint cosmic light, which presents itself as a series of spikes in the infrared spectrum, had no easily identifiable source. It seemed unrelated to any recognizable cosmic feature, like giant interstellar clouds, star-forming regions, or supernova remnants. It was ubiquitous and a bit baffling.

The likely culprit, scientists eventually deduced, was the intrinsic infrared emission from a class of organic molecules known as polycyclic aromatic hydrocarbons (PAHs), which, scientists would later discover, are amazingly plentiful; nearly 10 percent of all the carbon in the universe is tied up in PAHs.

Even though, as a group, PAHs seemed to be the answer to this mystery, none of the hundreds of PAH molecules known to exist had ever been conclusively detected in interstellar space.

New data from the National Science Foundation’s Green Bank Telescope (GBT) show, for the first time, the convincing radio fingerprints of a close cousin and chemical precursor to PAHs, the molecule benzonitrile (C₆H₅CN). This detection may finally provide the “smoking gun” that PAHs are indeed spread throughout interstellar space and account for the mysterious infrared light astronomers had been observing.

The results of this study are presented today at the 231st meeting of the American Astronomical Society (AAS) in Washington, D.C., and published in the journal Science.

The science team, led by chemist Brett McGuire at the National Radio Astronomy Observatory (NRAO) in Charlottesville, Virginia, detected this molecule’s telltale radio signature coming from a nearby star-forming nebula known as the Taurus Molecular Cloud 1 (TCM-1), which is about 430 light-years from Earth.

“These new radio observations have given us more insights than infrared observations can provide,” said McGuire. “Though we haven’t yet observed polycyclic aromatic hydrocarbons directly, we understand their chemistry quite well. We can now follow the chemical breadcrumbs from simple molecules like benzonitrile to these larger PAHs.”

Though benzonitrile is one of the simplest so-called aromatic molecules, it is in fact the largest molecule ever seen by radio astronomy. It also is the first 6-atom aromatic ring (a hexagonal array of carbon atoms bristling with hydrogen atoms) molecule ever detected with a radio telescope.

While aromatic rings are commonplace in molecules seen here on Earth (they are found in everything from food to medicine), this is the first such ring molecule ever seen in space with radio astronomy. Its unique structure enabled the scientists to tease out its distinctive radio signature, which is the “gold standard” when confirming the presence of molecules in space.

As molecules tumble in the near vacuum of interstellar space, they give off a distinctive signature, a series of telltale spikes that appear in the radio spectrum. Larger and more complex molecules have a correspondingly more-complex signature, making them harder to detect. PAHs and other aromatic molecules are even more difficult to detect because they typically form with very symmetrical structures.

To produce a clear radio fingerprint, molecules must be somewhat asymmetrical. Molecules with more uniform structures, like many PAHs, can have very weak signatures or no signature at all..

Benzonitrile’s lopsided chemical arrangement allowed McGuire and his team to identify nine distinct spikes in the radio spectrum that correspond to the molecule. They also could observe the additional effects of nitrogen atom nuclei on the radio signature.

“The evidence that the GBT allowed us to amass for this detection is incredible,” said McGuire. “As we look for yet larger and more interesting molecules, we will need the sensitivity of the GBT, which has unique capabilities as a cosmic molecule detector.”

The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under a cooperative agreement by Associated Universities, Inc.

The Green Bank Observatory (GBO, https://greenbankobservatory.org) is a facility of the National Science Foundation operated under a cooperative agreement by Associated Universities, Inc.

# # #

Reference: “Detection of the Aromatic Molecule Benzonitrile (c-C6H5CN) in the Interstellar Medium,” B. McGuire, et al., Science, Jan. 2018. [http://science.sciencemag.org/]

Contact:
Charles Blue
NRAO Public Information Officer
[email protected]
(434) 296-0314

Mike Holstine
Business Manager, Green Bank Observatory
+1 (304) 456-2011
[email protected]

In Other News…

IMAGE RELEASE: Moon’s Tycho Crater Revealed in Intricate Detail

The National Science Foundation’s Green Bank Observatory (GBO) and National Radio Astronomy Observatory (NRAO), and Raytheon Intelligence & Space (RI&S) have released a new high-resolution image of the Moon, the highest-ever taken from the ground using new radar technology on the Green Bank Telescope (GBT).

ACEAP Ambassador Heads into Space as First African-American Woman to Pilot Spacecraft

Astronomy in Chile Educator Ambassadors Program participant pilots SpaceX Dragon spacecraftToday Sian Proctor, a participant in the Astronomy in Chile Educator Ambassadors Program (ACEAP) has successfully piloted the Inspiration4 mission carrying her and three other...

NSF Awards Funding for Next-Generation VLA Antenna Development

The National Science Foundation (NSF) has awarded the National Radio Astronomy Observatory (NRAO) $23 million for design and development work on the Next Generation Very Large Array (ngVLA), including producing a prototype antenna.

Andean Science Diplomacy: Interview with Chile’s Ambassador to the U.S., Ambassador Silva

Ambassador Alfonso Silva Navarro leads Chile’s Embassy to the United States since September 2018. His extensive diplomatic career includes being the Chilean Ambassador to Canada, India, and Jamaica, as well as being the Director General on Foreign Affairs at Chile’s Ministry of Foreign Affairs.

NANOGrav & Green Bank Telescope Poised to Make Groundbreaking Discoveries of Gravitational Wave Universe

For the next three years, astronomers from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) will have increased access and new technologies to use on the National Science Foundation’s Green Bank Telescope (GBT) in their breakthrough scientific studies of gravitational waves.

Astronomers make first clear detection of a moon-forming disc around an exoplanet

Using the Atacama Large Millimeter /submillimeter Array (ALMA), in which the European Southern Observatory (ESO) is a partner, astronomers have unambiguously detected the presence of a disc around a planet outside our Solar System for the first time.

AUI and Accumen Partner to Increase Crisis Resilience to Natural and Manmade Disasters for Healthcare Sector

AUI and Accumen, Inc. announced they are partnering to provide services to improve crisis resilience to manmade and natural disasters for the healthcare sector at a historically challenging time.

New Scholarship Established by the AUI Board of Trustees

AUI and the National Radio Astronomy Observatory (NRAO) today announced the establishment of the AUI Board of Trustees NAC Bridge Scholarship Award.

2021 Jansky Lectureship Awarded to Mexican Astronomer

Associated Universities, Inc. (AUI) and the National Radio Astronomy Observatory (NRAO) have awarded the 2021 Karl G. Jansky Lectureship to Professor Luis F. Rodriguez of the National University of Mexico (UNAM).

Pride Month Statement

Pride Month is a time for celebration of LGBTQIA+ communities in commemoration of the Stonewall Uprising of 1969. At AUI, we celebrate an environment that is safe and welcoming to all, and the strength that our diversity brings us.

You are now leaving AUI

You will be redirected to the related partnering organization's website.

You will be redirected to
in 4 seconds...

Click the link above to continue or CANCEL