Dark Energy Detectives' cosmic map sheds light on dark matter

Posted Apr 13, 2015 by Robert Myles
An international team of scientists participating in the Dark Energy Survey have published the first of a series of dark matter maps of the cosmos.
Aerial photo of CTIO at cerro Tololo  Chile  a 4 meter telecope participating in the Dark Energy Sur...
Aerial photo of CTIO at cerro Tololo, Chile, a 4 meter telecope participating in the Dark Energy Survey. The Cerro Tololo Inter-American Observatory hosts the DES's Dark Energy Camera, one of the world’s most powerful digital cameras
Dark Energy Survey
The maps, created using one of the world’s most powerful digital cameras, are designed to probe the origin of the accelerating universe and help uncover the nature of dark energy.
They are the largest contiguous maps created at this level of detail. The project scientists hope they will improve our understanding of the role dark matter plays in the formation of galaxies. By analysing the “clumpiness” of the dark matter in the maps, scientists will be able to further examine the nature of mysterious dark energy, thought to be the reason the universe is continuing to expand at an accelerating rate.
In 2013 the Dark Energy Survey, bringing together more than 120 scientists from 23 institutions in the US, Spain, the UK, Brazil, and Germany, started work on a five-year mission to map a large portion of the southern sky in unprecedented detail. Their aim is to uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision.
The Dark Energy Survey (DES) evolved from the remarkable discovery, in 1998, by two teams of astronomers studying distant supernovae, that the expansion of the universe is speeding up. That appears to conflict with Einstein's theory of General Relativity which holds that gravity should be operating to slow down the universe’s expansion.
The first Dark Energy Survey map tracing the detailed distribution of dark matter across a large are...
The first Dark Energy Survey map tracing the detailed distribution of dark matter across a large area of sky. The red and yellow 'clumps' show regions with more dense matter. The map reflects the current picture of mass distribution in the universe where large filaments of matter align with galaxies and galaxy clusters. Clusters of galaxies are shown by gray dots with bigger dots denoting larger clusters.
Dark Energy Survey
To explain cosmic acceleration, cosmologists face two possibilities: Either 75 percent of the universe exists in an exotic form, now called dark energy, that exhibits a gravitational force opposite to the attractive gravity of ordinary matter, or General Relativity must be replaced by a new theory of gravity on cosmic scales.
The new map was released April 13 at a meeting of the American Physical Society in Baltimore, MD. To create the map, scientists used data captured by the Dark Energy Camera, at 570-megapixels, one of the world’s most powerful digital cameras. The Dark Energy Camera, roughly 100 times more powerful than a typical digital camera, is the primary instrument for the DES.
The camera, constructed and tested at the U.S. Department of Energy’s Fermi National Accelerator Laboratory, is now mounted on the 4-meter Victor M. Blanco telescope at the National Optical Astronomy Observatory’s Cerro Tololo Inter-American Observatory in Chile.
A number of scientists and institutions associated with the DES worked for over a year, validating and cross-checking the lensing maps.
Mysterious dark matter is thought to account for about 25 percent of everything that goes to make up our universe. Dark matter is invisible to even the most sensitive astronomical instruments since it doesn’t emit or block light. However, how dark matter impacts on the universe can be seen by examining a phenomenon called gravitational lensing.
Gravitational lensing is the distorting effect dark matter has when it bends light around distant galaxies. Understanding dark matter’s effects is part of the DES research program to quantify the role of dark energy, the ultimate aim of the DES.
“We measured the barely perceptible distortions in the shapes of about two million galaxies to construct these new maps,” commented Vinu Vikram, one of the DES researchers, now based at Argonne National Laboratory. “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,” Vikram added.
The dark matter map released today covers a mere 3 percent of the area of the sky that the DES hopes to document during the remainder of its five year mission. As DES researchers expand their search, they will be able to better test current cosmological theories by comparing the amounts of dark and visible matter.
As those theories go, since there’s much more dark matter in the universe than visible matter, galaxies should form where large concentrations of dark matter (and hence stronger gravity) are present. This is borne out by DES research to date: The maps show large filaments of matter along which visible galaxies and galaxy clusters lie and cosmic voids containing very few galaxies. Scientists hope follow-up studies, targeting some of the enormous filaments and voids as well as the enormous volume of data collected throughout DES will reveal more about this interplay between mass and light.
“Our analysis so far is in line with what the current picture of the universe predicts,” said Chihway Chang of ETH Zurich, one of the world’s leading universities for technology and the natural sciences, adding, “Zooming into the maps, we have measured how dark matter envelops galaxies of different types, and how together they evolve over cosmic time. We are eager to use the new data coming in to make much stricter tests of theoretical models.”
Over the next three years or so, through the work of the DES, while there’s no guarantee all the secrets of dark energy will be unlocked, should learn a lot more about this mysterious force.
Einstein would be fascinated!
You can follow development from the Dark Energy Survey on Twitter (@TheDESurvey) while each Monday, scientists working on DES — the Dark Energy Detectives — post the latest pictures on their Twitter feed.