In a strange case of cosmic detachment, astronomers have discovered a huge disk of hydrogen gas that surrounds a galaxy but does not appear to be involved in the galaxy's star-formation processes. The gas may be primordial material left over from the galaxy's formation, and that would provide an interesting natural laboratory for further study.

The dwarf galaxy, called UGC 5288, is much smaller than our Milky Way. In this combined radio and visible-light image, the bright white center object is the main galaxy, seen in visible light. The purple region is a giant hydrogen-gas disk detected by the National Science Foundation's Very Large Array (VLA) radio telescope.

In visible light, the elongated galaxy is about 6000 by 4000 light-years, but the hydrogen-gas disk is about 41,000 by 28,000 light-years. A light-year is the distance light travels in a year, about 6 trillion miles (10 trillion kilometers).

Astronomers wonder how the gas came to be in its present configuration. The disk shows no signs that the gas was either blown out of the galaxy by star formation or pulled out by a close encounter with another galaxy.

"You need the gas to make the stars, so we might have thought the two would be better correlated," said Martha Haynes, an astronomer at Cornell University. "This means we really don't understand how the star-forming gas and the stars themselves are related."

"This gas disk is rotating quite peacefully around the galaxy," said Liese van Zee of Indiana University. That means, she said, that the gas around UGC 5288 most likely is pristine material that never has been "polluted" by the heavier elements produced in stars.

"The lack of interaction between the large gas disk and the inner, star-forming region of this galaxy is a perplexing situation," van Zee said. "When we figure out how this has happened, we'll undoubtedly learn more about how galaxies form."

The galaxy is relatively nearby, at about 16 million light-years from Earth.

The observations were presented last week at a meeting of the American Astronomical Society. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

-- SPACE.com Staff

Credit: Van Zee, NOAO, NRAO/AUI/NSF