From Berkeley Lab: “Clocking an Accelerating Universe: First Results from BOSS” 

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Berkeley Lab

Berkeley Lab scientists are the leaders of BOSS, the Baryon Oscillation Spectroscopic Survey. They and their colleagues in the third Sloan Digital Sky Survey have announced the most precise measurements ever made of the era when dark energy turned on.

Julie Chao
March 30, 2012

“Some six billion light years ago, almost halfway from now back to the big bang, the universe was undergoing an elemental change. Held back until then by the mutual gravitational attraction of all the matter it contained, the universe had been expanding ever more slowly. Then, as matter spread out and its density decreased, dark energy took over and expansion began to accelerate.

Today BOSS, the Baryon Oscillation Spectroscopic Survey, the largest component of the third Sloan Digital Sky Survey (SDSS-III), announced the most accurate measurement yet of the distance scale of the universe during the era when dark energy turned on.

‘We’ve made precision measurements of the large-scale structure of the universe five to seven billion years ago – the best measure yet of the size of anything outside the Milky Way,’ says David Schlegel of the Physics Division at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), BOSS’s principal investigator. “We’re pushing out to the distances when dark energy turned on, where we can start to do experiments to find out what’s causing accelerating expansion.”

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BOSS measures the three-dimensional clustering of galaxies at various redshifts, revealing their precise distance, the age of the universe at that redshift, and how fast the universe has expanded. The measurement uses a “standard ruler” based on the regular variations of the temperature of the cosmic microwave background (CMB), which reveal variations in the density of matter in the early universe that gave rise to the later clustering of galaxies and large-scale structure of the universe today. (Click on image for best resolution. Credit: Eric Huff, the SDSS-III team, and the South Pole Telescope team. Graphic by Zosia Rostomian)

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For each 15-minute exposure of the deep sky, astronomers plug a thousand optical fibers into a plate that fits at the focal plane of the Sloan Telescope. Each fiber feeds the light of an individual galaxy to BOSS’s advanced spectrograph. (Photo by Dan Long, Senior Operations Engineer, Apache Point Observatory)

See the full article here.

A US Department of Energy National Laboratory Operated by the University of California

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