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


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

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

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

“To be even safer, we tried several independent signal processing techniques on the GBT and 20 meter results to try and remove the feature as if it were the instrumental background, rather than a actual signal, and neither of these methods succeeded in suppressing it, ”said researcher Philip Engelke.

1-4: narrow-line emission typical of the OH molecule of the spiral arms. 5: A new large and weak structure of the OH molecule – in and between the spiral arms. Credit: NSF / GBO / P.Vosteen

The researchers carried out another 100 hours of exhaustive observations at many different points in different parts of the galaxy and found that it was similar in shape and extent to other known components within the galactic structure. These observations had proven that the accidental discovery was a real thing.

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

The discovery dates back to 2012, when astronomer Ron Allen, a professor in the Department of Physics and Astronomy at Johns Hopkins University, came across broadcasts that led to the discovery.

However, Allen passed away in August 2020, just as his research was being written. So his former doctoral 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… he will be dearly missed.” Engelke added, who completed his PhD in 2019, “We were very lucky to have known him. Ron was really excited about this discovery, and I know he would have been proud of the result. Michael and I look forward to further research inspired by this discovery. ”

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

To find out more about the Green Bank Observatory science and 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 made up of a mysterious interstellar medium, about which scientists are learning even more. The major component of molecular gas in the interstellar medium is H2, but the H2 is generally undetectable! To map it, radio astronomers look for “tracers” in the form of signals from other molecules mixed with H2 in smaller amounts, and the standard tracer is carbon monoxide (CO). However, depending on the diffusion and the cold of 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 detected, and was there another method to trace this gas and confirm its existence?

In 2012, the astronomer Ron allen, a professor in the Department of Physics and Astronomy at Johns Hopkins University, unexpectedly discovered corresponding non-CO OH emissions while working on an unrelated project. As OH is also a gas molecule that occurs in clouds of molecular H2, this discovery hinted that there might be an abundant part of H2 not traced by CO, also called “CO-dark” molecular gas.

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

Later in 2015, while reviewing the data, Engelke noticed a bump-like feature, which he initially believed to be the outer arm of our Milky Way galaxy. Follow-up observations revealed a broad, weak, and broad feature across the line of sight. Allen and his team were intrigued, but suspected that this feature might be an instrumental by-product of the GBT itself, rather than an actual Galaxy feature. The researchers proposed a test: observe the feature with a completely independent telescope.

In 2018, 100 hours of independent observations were carried out using the Observatory’s tools 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 mainly used in educational projects, including the University of North Carolina SkyNet.


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