Image: TOM ABEL

New computer simulations are helping to fill in some of the details left out in Genesis¿namely, where all the light was coming from. According to a report published online last week by the journal Science, the very first protostar began forming deep within a cloud of hydrogen and helium that condensed from a nascent galaxy. (In the image at the right, the protostar is depicted forming from hotter material that cools as it collapses under its own gravity.) The modeling doesn't reveal exactly how big the star eventually became, physicist Michael L. Norman of the University of California in San Diego, a co-author of the report, explains, "but we're pretty confident it's going to be about a hundred solar masses." These results could account for the composition of stars visible today.

The authors' earlier modeling attempts offered the first glimpses of the molecular cloud collapsing. This time, however, they ran their simulations on a 16-processor SGI Origin 2000 supercomputer at the National Center for Supercomputing Applications in Illinois, which allowed them to resolve more detail in a larger virtual universe. According to Norman, this data and some additional work finished more recently answer astronomers' objections that if early stars were large, they would split apart due to instability or fail to form because they were spinning too fast. "We've said all along that we thought these first stars would be massive," Norman notes. "This closes a loophole, as it were."

The results also fit nicely with a few things scientists already know about stars. The cores of stars manufacture all the elements heavier than lithium, and they distribute these metals when they explode as supernovae. Even the oldest stars astronomers can see today, which date back to a universe about one billion years old, have at least some heavy elements in them¿and in the amounts one would expect after one round of supernovae, some have argued. A star as massive as the one the simulation predicts, Norman explains, "is going to go supernova within a few million years, and it will have produced plenty of heavy elements in the core before it does that."

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