River of Hydrogen May Be Fueling Nearby Galactic Star Formation

A river of hydrogen flowing through space and into a nearby galaxy is likely the first of its kind ever documented and may help astronomers explain how spiral galaxies maintain a steady pace of star formation.

The river was spotted with the National Science Foundation's Green Bank Telescope (GBT) by West Virginia University astronomer D.J. Pisano, who published an account of the observations in the Astronomical Journal.

"We knew that the fuel for star formation had to come from somewhere. So far, however, we've detected only about 10 percent of what would be necessary to explain what we observe in many galaxies," Pisano said. "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."

Pisano observed a faint river of hydrogen gas leading into the galaxy NGC 6946, which is about 22 million light years away from Earth on the border of the constellations Cepheus and Cygnus.

NGC 6946 is a much more active spiral galaxy than our own, the Milky Way, which forms stars at a slow, but steady pace. It is speculated that this river of hydrogen is what enabled the galaxy to churn out stars at its quicker pace.

The unique detection properties of the GBT allowed Pisano to observe the flow of hydrogen into the galaxy. Other telescopes that have observed the galaxy may have simply been too weak to register the faint traces of cold hydrogen creeping into NGC 6946.

The river-of-gas theory is consistent with the long-standing theory that larger galaxies can maintain a constant flow of hydrogen by siphoning it off smaller galaxies in their vicinity.

Future studies of the galaxy will help scientists get a better picture of what exactly is going on there and perhaps shed more light on the role that cold flows of hydrogen may play in the evolution of galaxies.