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Report: After the Big Bang, the Big Snowstorm
By Robert Roy Britt
Senior Science Writer
posted: 07:00 am ET
26 November 2002
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In the dead dark hours before dawn, it was growing colder by the minute. The sky was empty and quiet, amplifying the vastness unique to this place and time. Then a few snowflakes began to form, flung about sparsely but reaching into every corner of the darkness, silent and unseen. When light broke a warmth spread through the sky like hot chocolate into the belly. The snow melted and it seemed as if a whole new era had begun.This is not a Thanksgiving morning in Minnesota. This was the end of the dark age of our early universe.Denis Puy and Daniel Pfenniger of the Geneva Observatory looked at the thermodynamics of space after the Big Bang and before the first stars were born, along with the stuff that existed back then. They conclude, in a soon-to-be-published report, that hydrogen snow would have developed."The dark age "snowstorm" would have been just a passing flurry before the universe was flooded by the light of the first stars," Puy told SPACE.com. "Indeed the light produced by these stars is thought to have, shortly after, reheated the whole universe to high temperature, so melting any snowflake that would have formed." Like the dark ages of modern history, the cosmic dark age is a period about which little is known. Scientists can't even figure out exactly when or how it ended, but it seems to have run for at least half a billion years. It is a crucial stretch of time, because whatever went on then led to everything we know today -- the rules for star formation and galaxy creation were laid out.Here is what is assumed: The early universe was dense and hot, and as things spread out, they cooled down. Hydrogen was the primary ingredient then (it still dominates the universe today). Somewhere along the line, ripples showed up in an otherwise smooth fabric of space. Knots of material gathered together and began to grow.Puy and Pfenniger went back to 300,000 years after the Big Bang, when the first hydrogen molecules are thought to have developed from hydrogen atoms. About 500 million years after everything began, the researchers found, the temperature became cold enough for hydrogen atoms to freeze into ice grains or snow. While terrestrial snow is mostly a water-based structure, there are similarities with hydrogen snow. Both types of snow require something to freeze onto, some "impurity," as scientists call it. Earth's atmosphere is full of bits of stuff that fill this role. Puy said more work needs to be done to figure out what impurities might have been available in the early universe and when. He speculates, meanwhile, that snowflakes might have dotted the vast, growing universe for several hundred million years. During this time, the snow might have had a great impact on the creation of the first objects - and scientists don' t yet know what these things were."One of the great cosmology problems concerns the nature of the first objects: super massive structures (such as galaxy clusters or galaxies), or "small" objects such as stars," Puy points out. "For this reason it is crucial to know precisely the initial conditions of the formation of these objects." The universe's initial snowstorm might actually have done itself in. The existence of snowflakes might have increased the ability of the hydrogen to absorb background radiation and warm up, Puy figures.More light could be shed on the first snow, and thus on the origin of light, by two telescopes -- NASA's Next Generation Space Telescope and ESA's Herschel -- planned for later in this decade. The new study will be detailed in a future edition of the journal Astronomy and Astrophysics. | | | |
