Dwarf galaxies can be made with gas leftover from early Universe

Washington, Feb 19 : NASA's Galaxy Evolution Explorer has identified dwarf galaxies forming out of nothing more than pristine gas likely leftover from the early universe.

Dwarf galaxies are relatively small collections of stars that often orbit around larger galaxies like our Milky Way.

The findings surprised astronomers because most galaxies form in association with a mysterious substance called dark matter or out of gas containing metals.

The infant galaxies spotted by the Galaxy Evolution Explorer are springing up out of gas that lacks both dark matter and metals.

Though never seen before, this new type of dwarf galaxy may be common throughout the more distant and early universe, when pristine gas was more pervasive.

Led by David Thilker of the Henry A. Rowland Department of Physics and Astronomy at The Johns Hopkins University, a team of astronomers spotted the unexpected new galaxies forming inside the Leo Ring, a huge cloud of hydrogen and helium that traces a ragged path around two massive galaxies in the constellation Leo.

The cloud is thought likely to be a primordial object, an ancient remnant of material that has remained relatively unchanged since the very earliest days of the universe.

Identified about 25 years ago by radio waves, the ring cannot be seen in visible light.

According to Thilker, "This intriguing object has been studied for decades with world-class telescopes operating at radio and optical wavelengths. Despite such effort, nothing except the gas was detected. No stars at all, young or old, were found."

"But, when we looked at the ring with the Galaxy Evolution Explorer, which is remarkably sensitive to ultraviolet light, we saw telltale evidence of recent massive star formation. It was really unexpected. We are witnessing galaxies forming out of a cloud of primordial gas," he added.

"We speculate that these young stellar complexes are dwarf galaxies, although, as previously shown by radio astronomers, the gaseous clumps forming these galaxies lack dark matter," said Thilker.

"Almost all other galaxies we know are dominated by dark matter, which acted as a seed for the collection of their luminous components - stars, gas, and dust. What we see occurring in the Leo Ring is a new mode for the formation of dwarf galaxies in material remaining from the much earlier assembly of this galaxy group," he explained.