The Green Bank Telescope Discovering Interstellar Organic Molecules

aromatic molecule benzonitrile was detected by the GBT in the Taurus Molecular Cloud 1 (TMC-1). Credit: B. McGuire, B. Saxton (NRAO/AUI/NSF)
The aromatic molecule benzonitrile was detected by the GBT in the Taurus Molecular Cloud 1 (TMC-1). Credit: B. McGuire, B. Saxton (NRAO/AUI/NSF)

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 13-atom molecule with a 6-atom aromatic carbon 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.”


About benzonitrile – Vimeo video

Benzonitrile discovered in Taurus molecular cloud – Vimeo video

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

Charles Blue
NRAO Public Information Officer
(434) 296-0314

Paul Vosteen
Media Specialist; Education & Public Outreach
Green Bank Observatory

Swarm of Hydrogen Clouds Flying Away from Center of our Galaxy

A team of astronomers has discovered what appears to be a grand exodus of more than 100 hydrogen clouds streaming away from the center of the Milky Way and heading into intergalactic space.

This observation, made with the National Science Foundation’s Green Bank Telescope (GBT), may give astronomers a clearer picture of the so-called Fermi Bubbles, giant balloons of superheated gas billowing out above and below the disk of our galaxy.

hydrogen clouds expanding from center of Milky Way galaxy
Photo Source: S. Brunier; Design & Illustration: P. Vosteen

The results are presented today at the 231st meeting of the American Astronomical Society in Washington, D.C.

“The center of the Milky Way is a special place,” notes Jay Lockman, an astronomer at the Green Bank Observatory in West Virginia. “At its heart is a black hole several million times more massive than the Sun and there are regions of intense star birth and explosive star destruction.”

These energetic processes, perhaps individually or together, have generated a powerful cosmic “wind” that has blown two enormous bubbles above and below the disk of the Milky Way that are filled with gas at tens-of-millions of degrees. This superheated gas, however, shines feebly at radio, X-ray and gamma-ray wavelengths.

The bubbles appear prominently in observations made by NASA’s Fermi Gamma-ray Space Telescope, which is why astronomers refer to them as the Fermi Bubbles.

“One problem that hinders study of this hot cosmic wind is that the gas has such low density that its emission is very faint, so there is no practical way to track its motion,” notes Lockman. “This is where the hydrogen clouds come in.”

Just like a handful of dust thrown into the air can show the motion of wind on Earth, the hydrogen clouds can act as test particles revealing the flow of the hotter, invisible wind from the center of the Milky Way.

Neutral hydrogen gas, the principal component of these clouds, shines brightly at the radio wavelength of 21 centimeters. These hydrogen clouds were first discovered by a team led by Naomi McClure-Griffiths of the Australian National University using a radio telescope array in Australia. However, that survey was confined to a region just a few degrees around the galactic center, so it gave only limited information on the number and extent of these clouds.

New research with the 100-meter GBT greatly extends these observations.

A group led by Lockman, McClure-Griffiths, and Enrico DiTeodoro, who is also with the Australian National University, mapped a much larger area around the galactic center in search of additional hydrogen clouds that might be entrained in the nuclear wind. They found a gigantic swarm of more than 100 high-velocity gas clouds. The properties of these clouds allow the scientists to learn about the shape of the wind-blown region and the enormous energies that are involved.

“The signature of these clouds being blown out of the Milky Way is that their velocities are crazy,” said Lockman. “Gas motions in the Milky Way are usually quite regular and are dominated by the orderly rotation of the Galaxy. In the Fermi Bubbles we see clouds right next to each other on the sky that have velocities differing by as much as 400 kilometers per second.”

According to the researchers, the most likely explanation for these wildly differing velocities is that they’re traveling within a cone of material that is expanding upward and away from the galactic center, so the front portion is coming toward us and the back part is flying away.

By modeling the distribution and velocities of the clouds, the astronomers found that they would fill a cone stretching above and below the galaxy to a distance of at least 5,000 light-years from the center. The clouds have an average speed of about 330 kilometers per second.

Di Teodoro notes: “What is especially puzzling is that we have not yet found the edge of the swarm of clouds. Somewhere above the galactic center, the hydrogen clouds have to dissipate or become ionized. But we have not found that edge yet, so there’s still a lot to learn.”

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

Paul Vosteen
Media; Education & Public Outreach
Green Bank Observatory

60 years of Radio Astronomy in Green Bank

While the Green Bank Observatory celebrates its one-year anniversary in October, the location itself (Green Bank) is celebrating a much longer relationship with radio astronomy. Green Bank, West Virginia, was the first home of the National Radio Astronomy Observatory (NRAO) and we are celebrating 60 years of research and discovery this year!

Below is a list of some of our significant accomplishments and events over the last 60 years:

1957 – Dedication of the National Radio Astronomy Observatory
1958 – Dedication of the Tatel Telescope (85-1)
1958 – National Radio Quiet Zone established
1959 – Discovery of Jupiter’s radiation belts
1959-  First Green Bank summer students arrive
1960 – First Search for Extraterrestrial Intelligence–Project Ozma
1961 – Drake equation written and presented to the Symposium for Extraterrestrial Intelligence
1961 – Development of bolometers and mm-wave receivers/telescopes.
1962 – First 300’ Telescope observations
1964 – First Green Bank Interferometer observations
1965 – 140’ observations begin
1965 – First high signal to noise detection of radio recombination lines
1967 – First U.S. VLBI observation: Green Bank to Maryland
1967-1973 – Discovery of flat galactic rotation curves, implying dark matter
1968-  First detection of Zeeman splitting of hydrogen
1968 – First intercontinental interferometry: Green Bank to Sweden
1968 – First pulsar discovered in a supernova remnant (Crab Nebula)
1969 – First organic polyatomic molecule detected in interstellar space
1970 – First detection of radio novae
1971 – First long-chain molecule detected (HC3N)
1974 – Detection the black hole at the center of the Milky Way (Sgr A*)
1975 – First radio confirmation of Einstein’s relativistic bending of light
1977 – Determination of the Tully-Fisher relationship
1979 – GBI retires and is run by the naval observatory for earth orientation and timing
1985-1986 – 300’ Telescope 1400 MHz sky survey
1987 – First residential teacher workshop/ 40’ Telescope becomes dedicated educational instrument
1988 – 300’ Telescopes collapse
1989 – CBS 5 GHz survey of radio sources
1989 – Senator Robert C. Byrd sponsors an appropriation for the Green Bank Telescope (GBT)
1991 – GBT groundbreaking
1995 – 140’ 30th anniversary conference and celebration
1995 – 20-meter Telescope built by the Naval Observatory and begins measurement of Earth’s orientation and rotation
1997 – Operation of Green Bank OVLBI Earth station with VSOP
2000 – Green Bank Telescope dedication and first light
2001 – Most detailed radar image produced of Venus’s surface geography
2003 – Green Bank Science Center dedicated
2004 – Detection of a population of high-velocity hi clouds around Andromeda
2005 – High-resolution radar mapping of the Moon
2005 – Discovery of >20 millisecond pulsars in a globular cluster Terzan 5
2006 – Detection of the first interstellar anion
2006 – Discovery of the fastest millisecond pulsar, with a spin of 716 times/second
2006 – First light for 3mm GBT Observations (Mustang)
2006 – Best tests of general relativity from a double-pulsar system
2007 – Detection of the molten core of the planet Mercury
2007 – GBT track replaced
2007 – PAPER begins fabrication for Galford Meadow Array
2008 – First detection of pre-biotic molecules in space
2008 – First discovery of a pulsar by a high school student
2009 – Fabrication of PAPER antennas for deployment in South Africa
2009 – GBT achieves planned surface performance at 3mm
2009 – Discovery of the first radio pulsar/x-ray binary “missing link”
2011-Present – Launch of most successful low-frequency pulsar survey, the GBNCC Pulsar Survey
2010 – Measurement of the most massive neutron star known
2010 – First redshift determinations for the Herschel sub-mm galaxies
2010 – Development of GUPPI Pulsar Backend
2010 – Intensity mapping developed to study hydrogen at z~0.8
2010 – 50th anniversary of SETI conference
2010 – GBT receiver turret capability extended
2010 – First high angular resolution image of the Sunyaev-Zel’Dovich Effect
2011-Present – Ongoing discovery of millisecond pulsars in Fermi unassociated sources
2012 – Detection of the second >2 msun neutron star
2013 – Limits on the stochastic gravitational wave background
2014 – Mustang 1.5 deployed, with rotator
2014 – Discovery of only known millisecond pulsar in a stellar triple system
2014 – Mapping by GBT results in the identification of Laniakea Supercluster
2014 – Discovery of excess dust emission at 3mm in the Orion Integral Shaped Filament.
2015 – GBT determines Gravitational Constant uniform across the universe
2016 – GBT discovers pebble-sized proto-planets in Orion
2016 – Detection of Massive Gas “Smith Cloud” on collision with Milky Way
2016 – First detection of a chiral (handed) molecule in space
2016 – NANOGrav limits on the nHz gravitational wave background start to constrain binary supermassive black hole environments
2016 – Green Bank Observatory established
2016 – Mustang 223 feedhorn bolometer
2016 – First multi-pixel camera for GBT 3mm spectroscopy (Argus)
2017 – Commissioning of the most sensitive phased array feed in the world (FLAG)
2017 – Phased Array Feed commissioned on GBT
2017 – GBT beamformer 3mm results
2017 – GBT reveals “ageless” silicon that may indicate a well-mixed galaxy

Green Bank Telescope Aids in Finding Lost Spacecraft

image of the moon showing location of spacecraft. GBT received radar signal as an inset.
Credits: NASA/JPL-Caltech

Finding a tiny lost space-craft at a distance of 270,000 miles away may seem impossible, but NASA scientists have done just that. Using a new radar technique, they have located India’s Chandrayaan-1 spacecraft which has been lost since August 2009, the last time any communication was received from it. Chandrayaan-1, India’s first mission to the moon, is a very small cube about five feet (1.5 meters) on each side — about half the size of a smart car. JPL scientists used NASA’s 70-meter (230-foot) antenna at NASA’s Goldstone Deep Space Communications Complex in California to send out a powerful beam of microwaves directed toward the moon. Then the radar echoes bounced back from lunar orbit were received by the 100-meter (330-foot) Green Bank Telescope in West Virginia.

According to the NASA press release, the successful rediscovering of Chandrayaan-1 provides the start for a unique new capability. Ground-based radars using large antennas including the GBT could be used as a collisional hazard assessment tool and as a safety mechanism for spacecraft that encounter navigation or communication issues, in future robotic and human missions to the moon.

Read the full press release here.