Tenuous Cosmic Gas Cloud Revealed by New ALMA Observations

Astronomers have discovered the most tenuous molecular gas ever observed. They detected the absorption of radio waves by gas clouds in front of bright radio sources. This radio shadow revealed the composition and conditions of diffuse gas in the Milky Way galaxy.

In order to calibrate its systems, ALMA looks at objects emitting strong radio waves. On rare occasions, the signals from distant calibrator sources have specific radio frequencies absorbed out of them by foreground gas. This process is similar to how a piece of tinted glass casts a colored shadow when light passes through it. These absorptions features actually possess valuable information about the intervening gas clouds.

By examining data from 36 calibrator sources, the researchers discovered three new absorption systems and confirmed one previously known system. For one calibrator source, named J1717-337, the scientists found absorptions caused by ten different molecules.

Absorption systems allow researchers to investigate tenuous gas clouds. In fact, one of the clouds was the most diffuse gas clouds ever discovered in the Milky Way galaxy.

The findings reveal a bit more about our Milky Way galaxy and the features found within it. This, in turn, may tell scientists a bit more about the nearby universe

The findings are published in the journal Publications of the Astronomical Society of Japan.

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