A new supercomputer simulation shows how hydrogen and helium gas in the early universe might have collapsed to form the first generation of stars. The program zooms in on a growing clump (clockwise from upper left) to reveal a tight knot of gas in

A Baby Album of the Universe

ATLANTA--Scientists have used a supercomputer to look at page one in the photo album of stars in the universe, and this is what they see: brilliant giants up to 100 times bigger than our sun. These stars began lighting up the cosmos about 50 million years after the big bang, according to research presented here this week at a meeting of the American Physical Society.

Astronomers have long wondered what the first objects in the universe looked like. Theories predict that after the big bang, gravity slowly pulled parts of the expanding gas into clumps, but the agreement ends there. Some models show the clumps coalescing into Jupiter-sized bodies or small dim stars. Others predict titanic stars or even black holes. Computer simulations--often used to model clusters of galaxies later in cosmic history--were little help, because they lacked the 3D resolution needed to track the collapse of myriad parcels of gas into small primordial clouds.

Now, a team led by cosmologist Michael Norman of the National Center for Supercomputing Applications in Urbana-Champaign, Illinois, has broken that barrier. The team used "adaptive mesh refinement," in which the program zooms in on developing clumps of gas and increases the resolution only in those areas. In this way, the researchers can follow the growth of a nebulous blob until it forms a tight knot ready to spawn a star. The simulation indicated that most such knots were a few hundred times more massive than our sun. Some fraction of that mass would collapse into stars, Norman says.

As a result, most of the stars were giants that lived fast and died young, consuming their nuclear fuel within a few million years. Then, they blew up and began seeding the cosmos with the heavy elements forged in their cores, such as carbon, oxygen, and iron. However, turbulence might have split some gas into small stars--perhaps even some tiny enough to survive to this day, Norman says. "That's a possibility, but we have every indication that most of the initial stars were massive," he notes.

"This is the best work that has been done on seeing the conditions that led to the formation of the first stars," says astrophysicist Jeremiah Ostriker of Princeton University in New Jersey. "The higher resolution allows them to follow the process in far greater detail, essentially to the stellar scale."

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