Gas stream feeding Milky Way much larger than thought

Science : The Large and Small Magellanic Clouds have been losing gas in a stream that falls into their larger galactic neighbor, the Milky Way. The gas stream was easily detected because it contains neutral hydrogen, which emits radio waves. To find out whether the gas stream also contains ionized hydrogen, which is harder to detect, Andrew Fox of the Space Telescope Science Institute in Baltimore, Maryland, and his colleagues analyzed data from the Hubble Space Telescope. Ionized hydrogen should absorb UV light passing through the stream, so Fox’s team examined light from quasars and active galaxies behind the gas stream. They found that the stream contains about 2 billion solar masses of ionized hydrogen. Taking into account the presence of other light gases such as helium, the total mass of the stream is estimated to be about 3 billion solar masses. In comparison, the stream contains just 500 million solar masses of neutral hydrogen. The stream of gas will likely feed the creation of new stars in the Milky Way for several billion years.