Massive galactic structure discovered, by accident, with Green Bank Telescope in West Virginia

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Photos taken by GBO PR Specialist Jill Malusky, 7-30-20 Credit NSF/GBO 20

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GREEN BANK, W.Va. (WOWK) – Astronomers at the National Science Foundation’s Green Bank Telescope (GBT) in West Virginia discovered a massive, previously-unknown structure in the Milky Way galaxy, according to a paper published in The Astrophysical Journal in mid-June.

The first discovery happened with a smaller telescope but researchers had to bring in a larger, 20-meter telescope to confirm the unexpected observation.

Sometimes, in our galaxy, not everything is visible to the naked eye and that’s what is happening here. This discovery was made using radio spectrum. Essentially, the astronomers are able to see things with the world’s largest fully steerable radio telescope, which looks like a large dish. Since the GBT has a high level of sensitivity, it was able to detect this extremely large structure that’s made up of molecular gas, versus a physical moon or planet. Right now, the people doing the research believe the structure extends far into the distant parts of the Milky Way galaxy.

“To be even more sure, we tried several different independent signal processing techniques on the GBT and 20-meter results to attempt to remove the feature as if it were from the instrumental background, rather than a real signal, and none of these methods managed to remove it,” said researcher Philip Engelke.

1-4: Typical narrow-line emission from the OH molecule from spiral arms. 5: A new, broad, and faint structure from the OH molecule–in and between the spiral arms. Credit: NSF/GBO/P.Vosteen

The researchers went through another exhaustive 100 hours of observations at many different points across parts of the galaxy and found that it has a similar shape and extent of other components known about within the galactic structure. These observations had proven, the accidental finding was a real thing.

According to the GBT staff, “the existence of this massive structure has implications for star formation theories, as well as the structure, make-up, and total mass of the interstellar medium.”

The find dates back to 2012, when astronomer Ron Allen, a professor with the Physics and Astronomy Department of Johns Hopkins University, stumbled across emissions that led to the discovery.

However, Allen died in August 2020, just as his research was being drafted. So his former PhD students stepped in and finished the work for publication in the Astrophysical Journal.

Michael Busch said, “Ron was an incredible mentor, a brilliant astronomer, and a great friend to me… I will miss him dearly.” Engelke added, who completed his doctorate in 2019, “We were very lucky to have known him. Ron was truly excited about this discovery, and I know he would have been proud of the result. Michael and I look forward to continued research inspired by this discovery.” 

Photos taken by GBO PR Specialist Jill Malusky, 7-30-20 Credit NSF/GBO 20

To learn more about Green Bank Observatory science and to see research opportunities visit their website.

The Green Bank Observatory is a facility of the National Science Foundation and is operated by Associated Universities, Inc.

The Green Bank Observatory has more on the technical aspects of this massive structure:

The Universe is composed of a mysterious interstellar medium, which scientists are still learning more about. The major component of the molecular gas in the interstellar medium is H2, but the H2 is usually undetectable! To map it out, radio astronomers look for “tracers” in the form of signals from other molecules mixed with the H2 in smaller quantities, and the standard tracer is carbon monoxide (CO). However, depending on how diffuse and cold the H2 and CO gases are, they still might not be seen. In 2005, astronomers (Grenier et al.) found an excess of cosmic rays, of unknown origin, emanating from the disk of our Galaxy. Was it possible that these rays were a clue to large reserves of molecular gas not yet been detected, and was there another method to trace this gas and confirm its existence? 

In 2012, astronomer Ron Allen, a professor with the Physics and Astronomy Department of Johns Hopkins University, unexpectedly found OH emission without corresponding CO emission while working on an unrelated project. As OH is also a gas molecule that occurs in clouds of molecular H2, this finding hinted that there might be an abundant portion of H2 not traced by CO, also referred to as “CO-dark” molecular gas. 

Allen worked with Dave Hogg of National Radio Astronomy Observatory to create a new research program using the GBT to observe OH as an alternative tracer of H2. Philip Engelke, a new Ph.D. student at Johns Hopkins University, joined the project soon after. In 2015, the first results of this research were published, showing that OH indeed traces the “CO-Dark” component of H2 remarkably well. While it required long exposure times, the OH observations began filling in the gaps between previous CO observations, showing molecular gas as a major component in the structure of our Galaxy.

Later in 2015, while reviewing data, Engelke noticed a bump-like feature, which he initially thought corresponded to the Outer Arm of our Milky Way Galaxy. Follow-up observations revealed a large, faint, broad feature in the entire line of sight. Allen and team were intrigued, but suspected that this feature could be an instrumental by-product of the GBT itself, rather than an actual feature in the Galaxy. The researchers came up with a test: observe the feature with a completely independent telescope.

In 2018, 100 hours of independent observations were conducted using the Observatory’s 20-meter Telescope. Johns Hopkins PhD student Michael Busch joined Allen’s team and played a major role in this work. The 20-meter, a much smaller and older instrument, is primarily used in educational projects including the University of North Carolina’s SkyNet.

FROM: GreenBankObservatory.org

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