Sometimes it really does take the most sensitive telescopes in the world to find what was in front of us all along. That's why the Green Bank Telescope was so valuable in the discovery of star-forming gas around the spiral galaxy NGC 6946 this week.
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Galaxies continue to form stars from clouds of gas that collapse and become dense enough to start hydrogen fusion. In order to collapse in the first place, that gas has to be cold, or, more specifically, not having its atoms moving around too quickly and chaotically. Much of the gas in galaxies is too diffuse and fast-moving, or "warm," to do so, thus galaxies only transform a small percentage of their gas into stars at any given time.
Our Galaxy and galaxies like it make new stars at about the rate of one solar mass per year. The reservoirs of cold gas that fall onto galaxies only account for 10 percent of that gas, at least until now. Where does all the star forming material come from?
D.J. Pisano from West Virginia University used the Green Bank Telescope to find the missing gas as rivers of hydrogen falling onto the spiral galaxy NGC 6946. A deep search revealed enough gas in these filaments to account for the star-formation happening in that galaxy.