Scientists using telescopes at the Green Bank Observatory have accidentally discovered a massive, invisible structure inside our galaxy. This discovery is being well-received in the scientific community and will change the way that scientists study the formation of stars in the outer galaxy and may help them better understand where the matter the universe is made up of is distributed.
According to one of the scientists who made the discovery, Astrophysicist Dr. Philip Engelke, the planet Earth is floating in this widespread structure, as is the sun and all the planets and stars we can see.
It is a disk made out of a very thin gas, mostly hydrogen molecules, and fills in all the spaces between the arms of the galaxy and extends toward the outer galaxy.
“It wasn’t easy to detect, but it is there,” Engelke said. “We already know about clouds of molecular gas in the center of the galaxy and in the arms of the galaxy, but it’s a bit more mysterious to know how stars form on the outskirts of the galaxy where we haven’t observed as much of this kind of molecular gas in the interstellar medium.”
Additionally, the discovery helps scientists more accurately estimate the total mass of the interstellar medium in our galaxy, which contributes to the mass along with stars as well as the mysterious concept known as “dark matter,” to better understand how these mass components interrelate.
Engelke said that finding the structure, along with Michael Busch, Ronald J. Allen, and David E. Hogg, was an exciting time. Unfortunately, the man instrumental in finding this structure, Johns Hopkins University professor Ronald J. Allen, passed away last year.
“We were very lucky to have known him,” Engelke said. “Ron was truly excited about this discovery, and I know he would have been proud of the result.”
The molecular hydrogen gas is nearly invisible, which is why scientists must look for radio signals from other molecules mixed in in smaller quantities, called tracers. The usual tracer is CO (carbon monoxide), but in 2012, Allen unexpectedly found OH molecule signal without corresponding CO signal while working on an unrelated project. He worked with David Hogg of National Radio Astronomy Observatory to create a new research program using the Green Bank Telescope to observe OH as an alternative tracer of hydrogen. The first results of this research was published in 2015.
During the next run of observations, the scientists noticed a faint signal coming from between the arms of the Galaxy. In 2018, 100 hours of independent observations were conducted using the observatory’s 20-meter telescope to confirm that this signal was truly real and not an artifact of the first telescope. During this time, Johns Hopkins Ph.D. student Michael Busch joined Allen’s team and played a major role in this work.
These findings were published in The Astrophysical Journal on June 10.
“It was exciting,” Engelke said. “It was the product of several years of work. I think it was good that we were finally able to get this published.”
Michael Busch plans to continue working on follow-ups to this discovery after he finishes his Ph.D. Although Engelke said that he is working in a different job, he plans to continue work on this discovery in his spare time. The new goal is to see if a similar structure exists in the Andromeda Galaxy, the closest spiral galaxy to our own.