Scientists Don't Know Why More Gas Comes In Than Out Of The Milky Way

Scientists have been trying to understand what they describe as a recycling process inside the Milky Way. Supernovas and stellar winds blow gas out of the galactic disc, but that gas falls back onto the galaxy to form new generations of stars. Scientists were surprised to find that there is a surplus of incoming gas.

The team says that they expected to find a balance of gas coming in and going out of the galaxy. But a decade of Hubble ultraviolet data that has been collected shows that more gas comes into the Milky Way than is going out.

Scientists, for now, don't know what causes more gas to come in than out of the galaxy. The team says that one explanation is that the extra inflow of gas could be coming from the intergalactic medium. One scientist believes that the Milky Way is raiding gas "bank accounts" of small satellite galaxies using its larger gravitational pull to siphon away resources.

The team also notes that its survey looked only at cool gas; hotter gas may play a role as well, say the scientists. This study marks the best measurements yet of how fast gas flows in and out of the Milky Way. Astronomers knew that galactic gas reserves are replenished by inflow and depleted by outflow; this process is important because it regulates the formation of new stars and planets.

Future studies will explore the inflowing gas surplus. Future research will also try and determine if other large galaxies behave similarly to how the Milky Way behaves. The team says that it has enough data to audit the Andromeda Galaxy, which is the closest large galaxy to the Milky Way.