BOSS to help probe presence of dark energy in the universe

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Washington, September 21 : A major mapping program known as BOSS (Baryon Oscillation Spectroscopic Survey), started in midsummer 2008, would help to probe the presence of dark energy in the universe.

Investigating dark energy has emerged as one of the most crucial tasks of the Sloan Digital Sky Survey (SDSS), under which falls the latest survey.

Astrophysicist David Schlegel, since 2004 a member of the Physics Division at the U.S. Department of Energy's Lawrence Berkeley National Laboratory, is the principal investigator of BOSS.

Schlegel and his colleague Nikhil Padmanabhan first used the SDSS telescope to complete the largest three-dimensional map of the universe ever made until then: 8,000 square degrees of sky out to a distance of 5.6 billion light years, determining the clustering of 60,000 luminous red galaxies.

This program, part of SDSS-II, measured galactic distances to a redshift of z = 0.35 and detected the 500-million-light-year scale of BAO (baryon acoustic oscillations).

"We were mostly excited that we could make a measurement. We proved we had a ruler we could use," said Schlegel.

"With BOSS, we're going from a measurement to a much more precise measurement that we can use to constrain dark energy," said Padmanabhan.

BOSS will double the volume of space in which red luminous galaxies will be studied, observing 10,000 square degrees of sky out to redshifts of z = 0.7.

The galaxy sample will increase from 60,000 to 1.5 million. BOSS will also include a new kind of object, measuring up to 200,000 quasars at even more extreme redshifts of z = 2 or more.

"The epoch of the most common quasars was at redshifts between 2 and 3, just enough that we can still see them at optical wavelengths in the blue and ultraviolet," Schlegel said.

"BOSS will be the first look at dark energy at these redshifts. Only a few Type Ia supernovae have been found beyond redshift," he added.

According to Padmanabham, BOSS will be within a factor of 2 of the best possible map of BAO in the universe.

BOSS will be able to determine BAO with an accuracy approaching one percent, one of the most precise possible measurements of the expansion of the universe.

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