Credit: Artist's Illustration: NASA, ESA, and D. Player (STScI) Science: NASA, ESA, and A. Fox (STScI)

Astronomers have discovered an unexplained surplus of gas flowing into our Milky Way after conducting a galaxy-wide audit of outflowing and inflowing gas. Rather than a gas equilibrium and "balanced books," 10 years of data from NASA's Hubble Space Telescope show there is more gas coming in than going out.

It is no secret that the Milky Way is frugal with its gas. The valuable raw material is recycled over billions of years—thrown out into the galactic halo via supernovas and violent stellar winds, and then used to form new generations of stars once it falls back to the galactic plane. The surplus of inflowing gas, however, was a surprise.

Hubble distinguished between outflowing and inflowing clouds using its sensitive Cosmic Origins Spectrograph (COS), which detects the movement of the invisible gas. As the gas moves away it appears redder, while gas falling back toward the Milky Way is bluer.

The source of the excess gas inflow remains a mystery. Astronomers theorize that the gas could be coming from the intergalactic medium, as well as the Milky Way raiding the gas "bank accounts" of its small satellite galaxies using its considerably greater gravitational pull.

Provider: Space Telescope Science Institute

Image Source: https://hubblesite.org/contents/news-releases/2019/news-2019-46

Curator: STScI, Baltimore, MD, USA

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