River of Cold Hydrogen May Fuel Wild Star Birth In Nearby Galaxy

By Gabrielle Jonas on January 28, 2014 1:04 PM EST

This composite image contains three distinct features: the bright star-filled central region of galaxy NGC 6946 in optical light (blue), the dense hydrogen tracing out the galaxy’s sweeping spiral arms and galactic halo (orange), and the extremely diffuse and extended field of hydrogen engulfing NGC 6946 and its companions (red).
This composite image contains three distinct features: the bright star-filled central region of galaxy NGC 6946 in optical light (blue), the dense hydrogen tracing out the galaxy’s sweeping spiral arms and galactic halo (orange), and the extremely diffuse and extended field of hydrogen engulfing NGC 6946 and its companions (red).

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Functioning as a cosmic umbilical cord for the gestation of stars, a river of hydrogen may be fueling the frantic pace of star formation in a nearby galaxy, an astronomer from West Virginia University, said in last week's issue of The Astronomical Journal. Astronomers have long been looking for such a river of hydrogen, because galaxies are forming new stars at a fast-paced clip that would account for 90 percent more fuel than they're seeing. "Such gas may represent the so-called cold flows predicted by current theories of galaxy formation," wrote Dr. D. J. Pisano, the astronomer from West Virginia University who observed the filament of hydrogen running into a galaxy called NGC 6946. "Observations of NGC 6946 reveal a filamentary feature apparently connecting NGC 6946 with its nearest companions. This hydrogen filament was invisible in past interferometer observations."

To help account for the missing 90 percent fuel and thus "complete the census of hydrogen," Pisano used the Robert C. Byrd Green Bank Telescope to map the circumference of the "galactic environment" around NGC 6946 and another galaxy, NGC 2997. The discovery of this river of hydrogen is all the sweeter as that radio telescope was threatened last year with removal of funding by the National Science Foundation, and has been kept going partly with funds from the university itself, with the proviso that WVU astronomers would get extra telescope-time. The radio telescope's immense single dish and fortuitous location in the so-called "National Radio Quiet Zone," allowed Pisano to detect the glow emitted by neutral hydrogen gas connecting NGC 6946, located about 22 million light-years from Earth on the border of the constellations Cepheus and Cygnus, with its cosmic neighbors. Here's the telescope:

The Robert C. Byrd Green Bank Telescope, threatened with loss of funds, was kept going partly by West Virginia University, who saw to it that their astronomers got extra dish-time.
The Robert C. Byrd Green Bank Telescope, threatened with loss of funds, was kept going partly by West Virginia University, who saw to it that their astronomers got extra dish-time.


Astronomers have long theorized that massive galaxies could syphon off cold hydrogen from smaller, neighboring galaxies in impossibly long filaments. A filament or river of hydrogen, or "cold flow," could fuel the fast pace of star formation in galaxies lucky enough to have them. Sure enough, Pisano, observing the sprial galaxy NGC 6946 located about 22 light-years from Earth, detected just the sort of filamentary structure that could signify a cold flow.

As hydrogen gas from intergalactic space that has never been heated to extreme temperatures by a galaxy's star birth or supernova processes, the "cold flow" would indeed be frigid. But there's debate among astronomers as to whether the hydrogen is a halo emanating out from the galaxy or a river flowing into it. Earlier probes of the galactic neighborhood around NGC 6946 with the Westerbork Synthesis Radio Telescope in the Netherlands revealed an extended halo of hydrogen — common in spiral galaxies — perhaps ejected from the galaxy by intense star formation and supernova explosions.

If that were the case, however, there should be a "small but observable population of stars in the filaments," according to West Virginia University. Further studies will help to determine whether those filaments are star-studded (in which case they could come from a bump by NGC 6946 against another galaxy, for instance) or are indeed an an umbilical cord feeding young stars the cold hydrogen they require for sustenance.

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