Mapping 3D structure of Universe may shed new light on dark energy

Mapping 3D structure of Universe may shed new light on dark energy   Washington: Astronomers from the University of Arizona (UA) and 41 other institutions are beginning the most ambitious project yet to map the three-dimensional structure of the universe in a quest to understand dark energy.

“Making a three-dimensional map is essential to understanding why the universe is expanding at an ever-accelerating rate,” said UA astronomy professor Daniel Eisenstein, director of the Sloan Digital Sky Survey III, known as SDSS-III, a collaboration of 350 scientists.

The new SDSS-III mapping project, called the Baryon Oscillation Spectroscopic Survey, or BOSS, collected its first astronomical data - a milestone called achieving “first light” - on a thousand galaxies and quasars on Sept. 14-15.

The BOSS team uses new, extremely sensitive optical-infrared spectrographs on the Sloan Foundation 2.5-meter telescope at Apache Point Observatory in New Mexico.

Their goal is to collect spectra for 1.4 million galaxies and 160,000 quasars by 2014.

Measuring the spectra, or colors, of galaxies and quasars allows astronomers to determine how far away and how far back in time these celestial objects are.

“The data from BOSS will be the best ever obtained on the large-scale structure of the universe,” said BOSS principal investigator David Schlegel of the US Department of Energy’s Lawrence Berkeley National Laboratory.

In the early universe, cosmic matter - the protons and neutrons, or “baryons” - interacted with the light from the Big Bang to create pressure oscillations much like sound waves.

Just as sound waves compress air molecules in our atmosphere, these “baryon acoustic oscillations” created density variations as they traveled through the early universe.

When the universe was around 400,000 years old, conditions were finally cool enough to halt the propagation of the sound waves, and this left a “frozen” sound wave signature, according to UA astronomy professor Xiaohui Fan.

“We can see these frozen waves in the distribution of galaxies today,” Eisenstein said.

“The signature is that pairs of galaxies are somewhat more likely to be separated by 500 million light-years, rather than 400 million or 600 million light-years,” he added.

The sound wave signature today is expected to be about 500 million light-years long because the universe has greatly expanded since those early times, according to Fan.

“By measuring the length of the baryon oscillations, we can determine how dark energy has affected the expansion history of the universe,” Eisenstein said. “That, in turn, helps us figure out what dark energy could be,” he added. (ANI)