Map of universe offers clues to dark energy

Posted by Kate Taylor

The biggest-ever 3D map of the universe has been released, including more than 500,000 galaxies and 100,000 stars.

The third Sloan Digital Sky Survey (SDSS-III) has issued Data Release 9 (DR9), the first public release of data from the Baryon Oscillation Spectroscopic Survey (BOSS), giving spectra for 535,995 newly observed galaxies, 102,100 quasars, and 116,474 stars, as well as new information about objects in previous Sloan surveys.

The material's being made available to the public - anyone that can use it, says  David Schlegel of Berkeley Lab, BOSS's principal investigator.

"This is just the first of three data releases from BOSS," he says.

"By the time BOSS is complete, we will have surveyed more of the sky, out to a distance twice as deep, for a volume more than five times greater than SDSS has surveyed before - a larger volume of the universe than all previous spectroscopic surveys combined."

By then, it will have measured 1.5 million galaxies and at least 150,000 quasars, as well as many thousands of stars and other ancillary objects.

BOSS is designed to measure baryon acoustic oscillation (BAO), the large-scale clustering of matter in the universe. BAO began as rippling fluctuationsin the hot, dense soup of matter and radiation that made up the early universe.

But as the universe expanded it cooled, atoms formed and radiation went its own way. However, the density ripples have left their marks as temperature variations in the cosmic microwave background (CMB), where they can be detected today.

Schlegel describes BAO as an inconveniently sized ruler, requiring a huge volume of the universe just to fit the ruler inside.

But, he says, it's a precision tool for tracking the universe's expansion history, and for probing the nature of gravity and the mysterious dark energy that's causing expansion to accelerate.

The data's available here.