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Early universe may have had snowflakes
By Richard Stenger
(CNN) -- Before galaxies, stars or planets, exotic snowflakes fluttered through the universe in the first and extremely dark cosmic winter, astronomers theorize. The flurries, composed not of water ice but condensed hydrogen, could have appeared about 300,000 years after the Big Bang, two Swiss researchers said. While born unimaginably hot, the expanding universe would have cooled enough by then for the first hydrogen atoms to coalesce, possibly in the form of transitory flakes. "In my opinion, the likelihood is something like 50 percent," said physicist Daniel Pfenniger of the University of Geneva, whose hypothesis is presented in the November 12 online edition of the journal Nature. Hydrogen, the simplest and most abundant element, freezes at temperatures near absolute zero. The universe at the time, however, was thought to be around 5,500 degrees F (3,000 degrees C). So what made the cosmic flakes possible? Pfenniger and colleague Denis Puy of the University of Zurich think the answer is a precarious balancing act between cosmic cooling and cosmic expansion. The hydrogen atoms would have expanded as well, becoming colder than the surrounding space, possibly enough to freeze. The flakes might have been fleeting, absorbing radiation and melting soon after they formed. "There are several factors that can either enhance or destroy hydrogen freezing. Only further observational and theoretical research will allow us to determine which competing effects dominated," Pfenniger said. The first snow would not have been white. The universe was in the midst of the cosmic dark age, which lasted until about one billion years after the Big Bang when the first stars ignited. If any flakes were still around then, ultraviolet light from the young stars would have blasted them to bits, the pair said. Their report will be published in the journal Astronomy and Astrophysics and is now available at an online clearinghouse of scientific papers: http://xxx.lanl.gov/abs/astro-ph/0211393 One eminent astronomer thinks the theory is full of hot air. "I think the paper is wrong. The gas is so dilute that it would take far longer than the age of the universe for molecules to stick together," said Sir Martin Rees, a cosmologist at Cambridge University.
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