More Galactic Gas In Milky Way Than We Thought
June 11, 2013

Study Says There’s Much More Galactic Gas In Milky Way Than We Thought

Brett Smith for - Your Universe Online

The building blocks of stars, clouds of molecular gases, are strewn across the Milky Way, and a new survey from the European Space Agency (ESA) and NASA has found that scientists have been underestimating the amount of gas in the galaxy by about one-third.

According to a new report in journal Astronomy and Astrophysics, the discovery was made possible by the orbiting Hershel Space Observatory, a joint venture between the two space agencies.

"There is an enormous additional reservoir of material available to form new stars that we couldn't identify before," said study co-author Jorge Pineda of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.

"We had to go to space to solve this mystery because our atmosphere absorbs the specific radiation we wanted to detect," added co-author William Langer, principal investigator on the Herschel project. "We also needed to see far-infrared light to pinpoint the location of the gas. For both these reasons, Herschel was the only telescope for the job."

Because the gas molecules, which are mostly hydrogen, can´t be seen using conventional telescopes, researchers have been searching for molecules of carbon monoxide, which are typically found within the clouds, radiate light much more efficiently, and can be easily detected. However, if gas is just beginning to pool in a region, carbon monoxide is not typically present.

"Ultraviolet light destroys the carbon monoxide," explained Langer. "In the space between stars, where the gas is very thin, there is not enough dust to shield molecules from destruction by ultraviolet light."

Previous efforts have included other “tracers” in the search for gaseous hydrogen clouds, including dust emissions and the interaction between clouds and interstellar gamma rays. These efforts had led to theories that there might be more interstellar gas than previously thought, and the new observations from Herschel have confirmed these theories, according to the new report.

The study also relied on the use of a new tracer: ionized carbon. Observed lingering in these large but relatively empty spaces, ionized carbon has been used to spot hydrogen molecules. Because most of the emissions of ionized carbon are absorbed by the Earth´s atmosphere, Herschel´s orbit allowed the scientists to create a more detailed map of its locations and abundance in the galaxy.

"This is the first survey of ionized carbon across the Galactic Plane — where most of the Milky Way's stars and star-forming clouds are concentrated — that combines both high spectral and angular resolution," Pineda said.

"Thanks to Herschel's incredible sensitivity, we can separate material moving at different speeds," added co-author Paul Goldsmith, the NASA Herschel Project Scientist at JPL. "We finally can get the whole picture of what's available to make future generations of stars."

The Herschel“¯survey also showed that hydrogen gas is distributed in a curious way across the Milky Way. According to the scientists, a large quantity of hydrogen is located in a ring surrounding the center of the Galaxy at radii between 13,000 and 36,000 light-years. The ring extends much farther than previously traced molecular gas, which extended to a radius of only about 13,000 light-years.

The researchers said they currently plan to study the newly discovered gas deposits in greater detail in an attempt to trace the complete process of star formation.