ARLA/CLUSTER: China começou a construir o Maior Rádio Telescópio do Mundo

[João Gonçalves Costa]

[http://tbn2.google.com/images?q=tbn:3apeDyVy2Ud-kM:http://www.centralasiatraveler.com/cn/xj/cr/images/qh_m01_qinghai_map.jpg]<http://images.google.pt/imgres?imgurl=http://www.centralasiatraveler.com/cn/xj/cr/images/qh_m01_qinghai_map.jpg&imgrefurl=http://www.centralasiatraveler.com/cn/xj/cr/charklik-ruoqiang.html&usg=__GivMj6C4UXoaYRN1zhJHxaRO1Os=&h=834&w=1056&sz=299&hl=pt-PT&start=2&um=1&tbnid=3apeDyVy2Ud-kM:&tbnh=118&tbnw=150&prev=/images%3Fq%3D10,000%2Bantennas%2Bin%2BChina%2527s%2BXinjiang%2BProvince%26ndsp%3D20%26um%3D1%26hl%3Dpt-PT%26sa%3DN>[http://tbn2.google.com/images?q=tbn:4Emm4Bx1q4LwXM:http://www.dailygalaxy.com/photos/uncategorized/2008/08/03/123752main_pia03538browse_2.jpg]<http://images.google.pt/imgres?imgurl=http://www.dailygalaxy.com/photos/uncategorized/2008/08/03/123752main_pia03538browse_2.jpg&imgrefurl=http://www.dailygalaxy.com/my_weblog/astronomy/&usg=__jrwsKaCnNyjU0yyXi4Bi3cJ8aVw=&h=490&w=678&sz=54&hl=pt-PT&start=1&um=1&tbnid=4Emm4Bx1q4LwXM:&tbnh=100&tbnw=139&prev=/images%3Fq%3D10,000%2Bantennas%2Bin%2BChina%2527s%2BXinjiang%2BProvince%26ndsp%3D20%26um%3D1%26hl%3Dpt-PT%26sa%3DN>
Massive Radio-telescope in China to Explore 'Dark Age' of Early Universe<http://www.dailygalaxy.com/my_weblog/2008/08/vals-sunday-pos.html>

<http://www.dailygalaxy.com/photos/uncategorized/2008/08/03/123752main_pia03538browse_2.jpg> Astronomers in the U.S. and China are also building an enormous radiotelescope array consisting of about 10,000 antennas in China's Xinjiang Province. They plan to use it to map the first glowing "bubbles" that appear as radiation from galaxies begins to ionize the dense fog of hydrogen between them and light it up.

"The only way we're ever going to understand this is when the theoretical work that's progressing rapidly in this field meets up with the observations work, which is coming from the other direction" of the timeline, says Elizabeth Barton, an astronomer at the University of California at Irvine.

"It's a big puzzle," she adds, and the new results, which appear in Friday's edition of the journal Science, represent a small but important piece.

Researchers reported they have glimpsed - using 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 new study is part of a broader effort to understand the early years of the universe, after the big bang using computer simulations can help scientists understand events like the birth of the first stars in the universe. During much of the universe's first billion years, the awesome brilliance 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.

"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."

The model follows the simpler physics that ruled the early universe to see how cold clumps of gas eventually grew into giant star embryos.

"Until you put that physics in the code, you can't evaluate how the first protostars formed," said Lars Hernquist, an astrophysicist at Harvard University whose early-stars model is detailed in this week's issue of the journal Science. His remarks were made Wednesday during a press teleconference.

Mysterious "dark matter" provided the first gravitational impetus for hydrogen and helium gas to start clumping together, Hernquist said. The gas began releasing energy as it condensed, forming molecules from atoms, which further cooled the clump and allowed for even greater condensing.

Unlike previous models, the latest simulation takes this cooling process of "complex radiative transfer" into account, said Nagoya University astrophysicist Naoki Yoshida, who headed up the modeling project.

Eventually gravity could not condense the gas cloud any further, because the densely-packed gas exerted a pressure against further collapse. That equilibrium point marked the beginning of an embryonic star, called a protostar by astronomers.

Simulation runs show that the first protostar likely started with just 1 percent the mass of our sun, but would have swelled to more than 100 solar masses in 10,000 years.

"No simulation has ever gotten to the point of identifying this important stage in the birth of a star," Hernquist noted.

Until new tools can peer more deeply into that gap, simulations remain the only vehicles for exploring the transition.

The simulation is part of an international 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.

The research team 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 sphere of a 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.

The stimulation stops there, but additional calculations suggest that within 1,000 years, the proto-star would have grown into a star 10 times more massive than the sun. By 10,000 years, the star would have topped 100 times the sun's mass.

Such huge stars are thought to have lived only for about 1 million years, compared with an expected lifetime of roughly 10 billion years for the sun.

The new work also traces the formation of the first stable proto-stars. No star could form without these stable proto-stars, even in today's universe, Dr. Hernquist says. The researchers eventually hope to run the simulation all the way up through the point where protostars ignite into true stars.

Posted by Casey Kazan in http://www.dailygalaxy.com/my_weblog/
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