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Bright Lights From Dark Places

May 23, 2011 - 2:09pm

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Scientists at the Energy Department’s national labs are using black holes to illuminate the distant parts of the universe in detail. Specifically, scientists from the Sloan Digital Sky Survey (SDSS-III), of which the Department’s Lawrence Berkley and Brookhaven National Labs are both a part, have used quasars to construct the largest three-dimensional map of the universe ever made. Quasars are one of the most brilliant beacons in the universe. Powered by gigantic black holes at the heart of galaxies, their light casts shadows across the universe.

Scientists used the illumination of some 14,000 quasars about 10 to 12 billion light years away to create the new map. That ultra-galactic cartography is the first significant result from the Baryon Oscillation Spectroscopic Survey (BOSS), which is the primary survey of the SDSS-III, and is led by researchers at Berkeley. The map will be further enriched in density and coverage during the three and a half years remaining in the BOSS survey.

The BOSS map shows more than the location of distant lights; it illuminates the vast clouds of hydrogen gas that lie in the spaces in between. Light changes as it travels through those shadowlands, which gives scientists a sense of their place in space.

Clouds of gas shift the light in slightly different ways, so it isn’t easy to tease their signals out. Scientists call the resulting spectrum the “Lyman-alpha forest,” for its messy, wiggly structure. (Imagine trying to draw a composite sketch of the people in a packed nightclub where the only illumination comes from a few spotlights at the far back of the stage.)

But by combining the many messy spectra, scientists are able to tease the signals of specific gas clouds out. That’s important, since this is the first time those clouds have been mapped in three dimensions, and they may hold a good portion of the universe’s visible mass (more here). And in addition to revealing more of the universe in three-dimensions (which can make a huge difference in value – ask anyone who waited to watch Avatar in 2-D), the method also may prove an accurate measure of how the universe itself has expanded over time.

That’s because even light travels at a finite speed. So by looking outwards, scientists are also looking backwards, and the farther out they look, the younger becomes the face of Father Time. The universe has also expanded, from the pinprick of potential at its beginning to the starry expanse we see today. So by studying its expansion through the BOSS survey, Energy Department scientists are learning much more about how we got here today; as well as where we might be going tomorrow, and for the next few billion years.

Not bad for a bright light . . . from a black hole.

For more information on the Office of Science, please go to: http://www.science.energy.gov/.

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