Elusive dark matter mapped at cosmic scale

Researchers, led by an Indian-origin scientist, have produced a detailed map of the distribution of dark matter in cosmos, tracing the invisible substance by monitoring its gravitational effects on light.
Scientists on the Dark Energy Survey released the first in a series of dark matter maps of the cosmos.
These maps, created with one of the world's most powerful digital cameras, are the largest contiguous maps created at this level of detail and will improve our understanding of dark matter's role in the formation of galaxies.
Analysis of the clumpiness of the dark matter in the maps will allow scientists to probe the nature of the mysterious dark energy, believed to be causing the expansion of the universe to speed up.

The new maps were were created using data captured by the Dark Energy Camera, a 570-megapixel imaging device that is the primary instrument for the Dark Energy Survey (DES).
Dark matter, the mysterious substance that makes up roughly a quarter of the universe, is invisible to even the most sensitive astronomical instruments because it does not emit or block light.

But its effects can be seen by studying a phenomenon called gravitational lensing - the distortion that occurs when the gravitational pull of dark matter bends light around distant galaxies.
"We measured the barely perceptible distortions in the shapes of about 2 million galaxies to construct these new maps," said Vinu Vikram of Argonne National Laboratory (then at the University of Pennsylvania).

"They are a testament not only to the sensitivity of the Dark Energy Camera, but also to the rigorous work by our lensing team to understand its sensitivity so well that we can get exacting results from it," said Vikram, who led the study.
The dark matter map released makes use of early DES observations and covers only about three per cent of the area of sky DES will document over its five-year mission. The survey has just completed its second year.
As scientists expand their search, they will be able to better test current cosmological theories by comparing the amounts of dark and visible matter.

Those theories suggest that, since there is much more dark matter in the universe than visible matter, galaxies will form where large concentrations of dark matter (and hence stronger gravity) are present.
The maps show large filaments of matter along which visible galaxies and galaxy clusters lie and cosmic voids where very few galaxies reside.