Around 13 billion years ago, the first stars to form may have included a strange type unknown to science until now. Among the glowing beacons of ordinary stars were "dark stars," according to research by a University of Utah scientist and two colleagues, which is poised to open a new chapter in the understanding of cosmology.

Perhaps some dark stars eventually collapsed into black holes, regions that are so massive that space and time are distorted and light cannot escape. But some dark stars may still be around as gigantic gaseous clouds 400 to 200,000 times larger than the sun and invisible except in the infrared.

"We're working on how long they last," said Paolo Gondolo, associate professor of physics at the U. and author of the study, "and the answer depends on the amount of material that surrounds the dark star."

The study will be published in December by Physical Review Letters. Besides Gondolo, authors are Katherine Freese of the University of Michigan, Ann Arbor, and graduate student Douglas Spolyar of the University of California at Santa Cruz.

Their work explains how "dark matter" may have influenced the early universe. Dark matter is known through gravitational effects on galaxies. It permeates space but its nature is not understood.

One idea is that dark matter involves particles called weekly-interacting massive particles (WIMPs). So far, no accelerator has found WIMPS, but theory holds that they exist and will annihilate each other when the particles are too close together.

"There were many, many WIMPs in the early universe; it was very dense," Gondolo said. Stars began to form as hydrogen and helium gas condensed into ever-shrinking clouds.

As gas contracted, it "dragged the dark matter with it," he said. Dark matter particles destroyed each other and released high-energy radiation. The radiation warmed the clouds enough to prevent them from collapsing into normal, bright stars.

"You end up with a cold cloud of helium and hydrogen that glows in infrared (heat energy) but otherwise is not a star," he said.

But other gas clouds without as much pressure from radiation "just will collapse into a bright star."

What happened to the dark stars? Those with the right amount of fuel may last as long as the universe.

Others could have a great deal more gas drawn onto them through gravity. The concentration may become so massive that gravity causes it to rapidly collapse, and it becomes a black hole. "It would solve a puzzle of black holes in the early universe," he said.

Gondolo said the findings were so unusual that "at the beginning I didn't trust them. I thought it was strange. Nobody had looked into this and found such a thing."

He and others rechecked the calculations and the reasoning behind the theory. "We had independent checks that what we were doing is right," Gondolo said. "We came to the same conclusion."

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