How matter clumps together in the universe

For the first time, astronomers claim to have used visual data from nearly a million luminous galaxies for the most accurate calculation yet of how matter clumps together in the universe.

Last Updated: Jan 15, 2012, 18:44 PM IST

Washington: For the first time, astronomers claim to have used visual data from nearly a million luminous galaxies for the most accurate calculation yet of how matter clumps together in the universe.

Using one of the biggest 3-D colour maps of the universe, a team led by the US Department of Energy`s Lawrence Berkeley National Laboratory has done the calculation -- from the time when the universe was only half its present age until now.

"The way galaxies cluster together over vast expanses of the sky tells us how both ordinary visible matter and underlying invisible dark matter are distributed, across space and back in time," said Shirley Ho, who led the team.

"The distribution gives us cosmic rulers to measure how the universe has expanded, and a basis for calculating what`s in it: How much dark matter, how much dark energy, even the mass of the hard-to-see neutrinos it contains. What`s left over is the ordinary matter and energy we`re familiar with," he said.

For their research, the astronomers first selected 900,000 luminous galaxies from among over 1.5 million such galaxies gathered by the Baryon Oscillation Spectrographic Survey, or BOSS, the largest component of the still-ongoing SDSS III.

The galaxies chosen for this study populate the largest volume of space ever used for galaxy clustering measurements.

Their brightness was measured in five different colours, allowing the redshift of each to be estimated.

"By covering such a large area of sky and working at such large distances, these measurements are able to probe the clustering of galaxies on incredibly vast scales, giving us unprecedented constraints on the expansion history, contents, and evolution of the universe," said team member Martin White.

"The clustering we`re now measuring on the largest scales also contains vital information about the origin of the structure we see in our maps, all the way back to the epoch of inflation, and it helps us to constrain -- or rule out -- models of the very early universe," he added.

After augmenting their study with information from other data sets, the team derived a number of such cosmological constraints, measurements of the universe`s contents based on different cosmological models.

Among the results, the astronomers found that dark energy accounts for 73 per cent of density of the universe, according to the findings which are to appear in the `Astrophysical Journal`.

PTI