The giant 'space river' of Hydrogen that could show why spiral galaxies keep spewing out stars Unprecedented insight into how galaxies like our own Milky Way form new stars Very faint, very tenuous filament of gas is streaming into the nearby galaxy NGC 6946 - just 22 million miles from Earth Astronomers have spotted a giant river of hydrogen in space - and say it could be what gives spiral galaxies their ability to keep spewing out stars. They say it could give an unprecedented insight into how galaxies like our own Milky Way form new stars - and why some are far more productive than others. The groundbreaking discovery helps explain the mystery that had baffled astronomers. The bright star-filled central region of galaxy NGC 6946 is shown in blue, while the dense hydrogen tracing out the galaxy's sweeping spiral arms and galactic halo is orange, and the extremely diffuse and extended 'river' of hydrogen engulfing NGC 6946 and its companions is red The very faint, very tenuous filament of gas is streaming into the nearby galaxy NGC 6946 NGC 6946 is located approximately 22 million light-years from Earth on the border of the constellations Cepheus and Cygnus. It is an active galaxy, though less-so than more extreme starburst galaxies, researchers said. 'We knew that the fuel for star formation had to come from somewhere,' said astronomer D.J. Pisano from West Virginia University. 'So far, however, we've detected only about 10 percent of what would be necessary to explain what we observe in many galaxies.' A leading theory is that rivers of hydrogen - known as cold flows - may be ferrying hydrogen through intergalactic space, clandestinely fueling star formation. But this tenuous hydrogen has been simply too diffuse to detect, until now. Using the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT), D.J. Pisano from West Virginia University has discovered what could be a never-before-seen river of hydrogen flowing through space. The very faint, very tenuous filament of gas is streaming into the nearby galaxy NGC 6946. Spiral galaxies, like our own Milky Way, typically maintain a rather tranquil but steady pace of star formation. Others, like NGC 6946, which is located approximately 22 million light-years from Earth on the border of the constellations Cepheus and Cygnus, are much more active, though less-so than more extreme starburst galaxies. This raised the question of what is fueling the sustained star formation in this and similar spiral galaxies. Messier 101, the gigantic Pinwheel galaxy, one of the best known examples of grand design spirals. researchers believer the new hydrogen river discovery could explain why spirals continue to produce stars. Using the GBT, Pisano was able to detect the glow emitted by neutral hydrogen gas connecting NGC 6946 with its cosmic neighbors. This signal was simply below the detection threshold of other telescopes. The GBT's unique capabilities, including its immense single dish, unblocked aperture, and location in the National Radio Quiet Zone, enabled it to detect this tenuous radio light. Astronomers have long theorized that larger galaxies could receive a constant influx of cold hydrogen by syphoning it off other less-massive companions. In looking at NGC 6946, the GBT detected just the sort of filamentary structure that would be present in a cold flow, though there is another probable explanation for what has been observed. It's also possible that sometime in the past this galaxy had a close encounter and passed by its neighbors, leaving a ribbon of neutral atomic hydrogen in its wake. If that were the case, however, there should be a small but observable population of stars in the filaments. Further studies will help to confirm the nature of this observation and could shine light on the possible role that cold flows play in the evolution of galaxies.