This illustration shows gas rising and falling in and out of the Milky Way galaxy using Hubble's COS instrument. With 10 years of data from COS, astronomers have found that there is more gas coming into our galaxy than leaving it.

Astronomers have discovered a strange surplus of gas in the Milky Way galaxy.

Using 10 years of data from NASA's Hubble Space Telescope, the team of astronomers concluded that there is more gas coming into our galaxy than leaving it. Rather than an equilibrium of gas entering and escaping, there is a significant imbalance, though the team behind this finding has not yet found the source for this gaseous disparity.

The researchers used data from Hubble's Cosmic Origins Spectrograph (COS), which allows the space telescope to study objects that absorb or emit light and determine aspects such as their temperature, chemical makeup, velocity and density. With COS, the team could observe and track the movement of gases in the galaxy: the gases appear redder as they move away from our galaxy, and bluer as they get closer through the phenomena known as redshift and blueshift .

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This allowed the researchers to see that there was more "blue" (entering) gas than "red" (exiting) gas. Although the researchers have not pinpointed the source of this imbalance, they think that it could possibly be caused by one of three things.

First, the astronomers think that this excess gas could be coming from the interstellar medium. Second, they suggest that the Milky Way is using its impressive gravitational pull to swipe gas from smaller, nearby galaxies, according to a statement .

Additionally, seeing as this study considered only cool gases, researchers think that hotter gases might also contribute to this finding.

Gases leave our galaxy when events like supernovae and stellar winds push them out of the Milky Way's galactic disk. When gases fall back into our galaxy, they contribute to the formation of new stars and planets. So the balance between the inflow and outflow of gases is important to regulating how objects such as stars form in galaxies like ours.

"Studying our own galaxy in detail provides the basis for understanding galaxies across the universe, and we have realized that our galaxy is more complicated than we imagined," co-author Philipp Richter of the University of Potsdam in Germany said in the statement.

This research will be published in a study in The Astrophysical Journal.