From Berkeley Labs: “Measuring the Distant Universe in 3-D”
Berkeley Lab-led BOSS proves it can do the job with quasars
May 01, 2011
“The biggest 3-D map of the distant universe ever made, using light from 14,000 quasars — supermassive black holes at the centers of galaxies many billions of light years away — has been constructed by scientists with the third Sloan Digital Sky Survey (SDSS-III).
The map is the first major result from the Baryon Oscillation Spectroscopic Survey (BOSS), SDSS-III’s largest survey, whose principal investigator is David Schlegel of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab). The huge new map was presented at the April meeting of the American Physical Society in Anaheim, CA, by Anže Slosar of Brookhaven National Laboratory.
BOSS is the first attempt to use baryon acoustic oscillation (BAO) as a precision tool to measure dark energy. Baryon oscillation refers to how matter clumps in a regular way throughout the universe, a physical manifestation of the expansion of the universe. Until now, 3-D maps showing this oscillation have been based on the distribution of visible galaxies. BOSS is the first survey to map intergalactic hydrogen gas as well, using distant quasars whose light is produced by supermassive black holes at the centers of active galaxies.
‘ Quasars are the brightest objects in the universe, which we use as convenient backlights to illuminate the intervening hydrogen gas that fills the universe between us and them,’ Slosar says. ‘ We can see their shadows, and the details in their shadows’ – specifically, the absorption features in their spectra known as the Lyman-alpha forest – ‘ allowing us to see how the gas is clumped along our line of sight. The amazing thing is that this allows us to see the universe so very far away, where measuring positions of individual galaxies in large numbers is impractical.
BOSS is extending the existing Sloan Digital Sky Survey map of the universe based on galaxies, center, into the realm of intergalactic gas in the distant universe, using the light from bright quasars (blue dots). (Sloan Digital Sky Survey)
See the full article here.