Scientists simulate early cosmos, find gigantic stars
New study is part of a broader effort to understand the early years of the universe, after the big bang.
For much of the universe's first billion years, the searing brightness born of the big bang faded to black. This dark age represents the least-understood chapter in the history of the cosmos scientists have compiled.Skip to next paragraph
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On Friday, researchers report they have glimpsed – via computer simulations – the birth of the first small, stable clumps of gas that would have served as seeds for the first generation of stars. Within 10,000 years, the scientists say, these seeds would blossom into blazing orbs at least 100 times more massive than the sun.
The simulation is part of a broad effort to fill the dark-age gap. Astronomers worldwide are pushing ground-based optical telescopes to their limits, building vast radiotelescope arrays and looking to a new generation of space- and ground-based telescopes to probe this crucial period.
The nuclear furnaces in the first stars would have formed the first atoms of carbon, silicon, oxygen, and other heavy elements, researchers hold. These elements would become incorporated into later generations of stars, which in turn would add their contributions to the chemical inventory.
Over time, clusters of stars would form galaxies whose combined radiation would eventually shift the cosmos from opaque to transparent. The heavier elements the stars forged and launched into the cosmos would form basic organic and inorganic molecules, and become the raw material for planets.
"We have a good understanding of what the universe looked like shortly after it originated about 14 billion years ago. We also have a good idea of what the universe looks like now," says Lars Hernquist, a Harvard University astrophysicist and member of the team. "But there's a significant gap in our understanding of how the universe made this transition from what it looked like after the big bang to how it appears to us today."
Until new tools can peer more deeply into that gap, simulations remain the only vehicles for exploring the transition.
In a young, dark universe
The research team, led by Nagoya University's Naoki Yoshida, started with a universe dominated by recently discovered dark energy and by cold dark matter, which astronomers currently detect by its gravitational influence on matter they can see. Hydrogen dominates the small percentage of "normal" matter in this young, denser universe. It's in a form that renders it opaque to light.
The simulation picks up the story when the universe was roughly 300 million years old and 20 times more compact that it is today. The afterglow of the big bang had long since faded. Subtle variations in the density of dark matter across space led to regions where dark matter was more dense than others.
The simulation focuses on one of these denser areas, or halos. There, dark matter's enhanced gravity corrals hydrogen. The hydrogen cloud undergoes alternate periods of heating and cooling as it contracts due to gravitational collapse. It also shifts from cloud to flattened disk and finally to a stable, spherelike proto-star.
At this stage, with 1 percent of the sun's mass (or about 10 times Jupiter's mass), the proto-star's internal temperature has risen high enough to generate an outward pressure that prevents further collapse.