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DES Scientists Carry Out Ultraprecise Measurement of Dark Matter in Cosmos

Consider sowing a single seed and accurately estimating the correct height of the tree that grows from the seed. Moreover, visualize a journey to the future to capture photographic evidence that the estimation was correct.

Map of dark matter made from gravitational lensing measurements of 26 million galaxies in the Dark Energy Survey. The map covers about 1/30th of the entire sky and spans several billion light-years in extent. Red regions have more dark matter than average, blue regions less dark matter. CREDIT: Chihway Chang of the Kavli Institute for Cosmological Physics at the University of Chicago and the DES collaboration.

Taking the seed to be the early universe and the tree to be the universe at present, one can have a vague idea of the work carried out by the Dark Energy Survey (DES) collaboration. DES Researchers have reported the most precise measurement of the large-scale structure of the present-day cosmos made to date, at the American Physical Society Division of Particles and Fields meeting at the U.S. Department of Energy’s (DOE) Fermi National Accelerator Laboratory.

Such measurements of the “clumpiness” (i.e. distribution) and amount of dark matter in the current universe were performed at an accuracy that, for the first time, contends the speculation made by the European Space Agency’s orbiting Planck observatory from the early universe. The new DES outcome, or the tree in the aforementioned metaphor, closely matches the “forecasts” of the Planck measurements of the remote past, or the seed, thus enabling the Researchers to gain insights into the manner in which the universe has evolved in more than 14 billion years.

This result is beyond exciting. For the first time, we’re able to see the current structure of the universe with the same clarity that we can see its infancy, and we can follow the threads from one to the other, confirming many predictions along the way.

Scott Dodelson, Fermilab

Particularly, this outcome validates the theory which states that nearly 26% of the universe is formed of strange dark matter and that an invisible dark energy fills the outer space, where the dark energy speeds up the expansion of the universe and fills almost 70% of the universe.

Ironically, the extensive clumpiness of the universe can be easily measured in the remote past than measuring it at present. During the period of the first 400,000 years after the Big Bang, a glowing gas filled the universe, where the light from this gas is present even today. Planck’s portrayal of such a cosmic microwave background radiation offers a glimpse of universe in the distant past. From that time, the dark matter’s gravitational pull has attracted mass together and rendered the universe clumpier over these years. However, dark energy has worked against this and has been ripping matter apart. Planck’s portrayal can be used by Cosmologists as the initial step in accurately computing the manner in which this conflict has happened in more than 14 billion years.

The DES measurements, when compared with the Planck map, support the simplest version of the dark matter/dark energy theory. The moment we realized that our measurement matched the Planck result within 7 percent was thrilling for the entire collaboration.

Joe Zuntz, the University of Edinburgh

The 570 megapixel Dark Energy Camera, which is the most powerful prevalent camera with the ability to acquire digital images of light from galaxies located nearly 8 billion light-years from our planet, is the principal equipment for DES. The camera was developed and investigated at Fermilab, the primary laboratory on the Dark Energy Survey. It is erected on the 4 m Blanco telescope of National Science Foundation, which is part of the Cerro Tololo Inter-American Observatory in Chile, a subsidiary of the National Optical Astronomy Observatory. Processing of the DES data is performed at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign.

The DES Researchers have been using the camera for 5 years to map one-eighth of the space in an unmatched way, where the fifth observation year will start in August. The new outcomes reported on 2nd August 2017 include data gathered in just the first year of the survey, that is, by mapping one-thirtieth of the space.

It is amazing that the team has managed to achieve such precision from only the first year of their survey. Now that their analysis techniques are developed and tested, we look forward with eager anticipation to breakthrough results as the survey continues.

Nigel Sharp, Director of the National Science Foundation Program

The DES Researchers applied two techniques for measuring the dark matter. The first technique involved producing maps of positions of galaxies as tracers. The second technique was known as gravitational lensing, which involved accurate measurement of the shapes of nearly 26 million galaxies to carry out direct mapping of the dark matter patterns distributed over billions of light-years.

In order to carry out such highly accurate measurements, the DES Scientists formulated innovative techniques to discover the minute lensing distortions of the images of galaxies, which are invisible to the human eye, thus making revolutionary progress in achieving an in-depth knowledge of these cosmic signals. During the course of their research, they developed the most elaborate model for observing dark matter in the universe ever noticed. The size of the new dark matter map is nearly 10 times that of the map released by DES in the year 2015. Ultimately, the map will turn out to be three times larger than at present.

It’s an enormous team effort and the culmination of years of focused work,” stated Erin Sheldon, a Physicist at the DOE’s Brookhaven National Laboratory, who co-created the new technique for observing lensing distortions.

The current outcomes and those from the first year of the Dark Energy Survey were reported online on 2nd August 2017 and presented as part of a lecture by Daniel Gruen, NASA Einstein fellow at the Kavli Institute for Particle Astrophysics and Cosmology at DOE’s SLAC National Accelerator Laboratory. The lecture is part of the APS Division of Particles and Fields meeting at Fermilab and was broadcast live.

The outcomes will also be reported at SLAC at the TeV Particle Astrophysics Conference in Columbus, Ohio, on 9th August 2017 by Kavli fellow Elisabeth Krause of the Kavli Insitute for Particle Astrophysics and Cosmology; and at the International Symposium on Lepton Photon Interactions at High Energies in Guanzhou, China, on 10th August 2017 by Michael Troxel, Postdoctoral Fellow at the Center for Cosmology and AstroParticle Physics at Ohio State University. Daniel Gruen, Elisabeth Krause, and Michael Troxel are Co-ordinators of DES science working groups and played significant parts in the investigations.

The Dark Energy Survey has already delivered some remarkable discoveries and measurements, and they have barely scratched the surface of their data. Today’s world-leading results point forward to the great strides DES will make toward understanding dark energy in the coming years.

Nigel Lockyer, Director, Fermilab

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