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Supercomputer Helps Researchers Map Space and Dark Matter

10 August 2017

Researchers have reached a significant milestone in mapping the growth of the universe from infancy to today with the help of an Ohio supercomputer.

The new research was released on August 3rd and confirmed a simple but puzzling theory. The theory says that the universe is composed of only 4 percent ordinary matter, 26 percent mysterious dark matter and the last 70 percent is mysterious dark energy that can cause the accelerating expansion of the universe.

The researchers from The Ohio State University and their colleagues from the Dark Energy Survey (DES) based their findings on data collected during the first year of DES, which covers more than 1,300 square degrees, about 6,000 full moons, of the sky. DES uses a Dark Energy Camera mounted on the Blanco 4m telescope at the Cerro Tololo Inter-American Observatory high in the Chilean Andes.

The Ohio Supercomputer Center was critical to getting the research done quickly, according to Klaus Honschied, Ph.D., professor of physics and leader of the Ohio State DES group. His computational specialists, Michael Troxel and Nial MacCrann, used about 300,000 core hours on OSC’s Ruby Cluster though condo arrangement between OSC and Ohio State’s Center of Cosmology and Astro-Particle Physics (CCAPP).

The team uses OSC’s Anaconda environment for standard work. Anaconda is an open source package of the Python and R programming languages for large-scale data processing, predictive analytics, and scientific computing. The group uses its own software to evaluate the multidimensional parameter space by using Markvo Chain Monte Carlo techniques, which are used to generate fair samples from a probability. The team ran validation code, or null tests, or object selection and fitting code to extract information about objects in the images gathered by simultaneously fitting the same object in the available exposures of the particular object.

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. Image credit: Chihway Chang of the Kavli Institute for Cosmological Physics at the University of Chicago, and the DES collaboration. (OSC)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. Image credit: Chihway Chang of the Kavli Institute for Cosmological Physics at the University of Chicago, and the DES collaboration. (OSC)

Most of the team’s 4 million computational allocations are at the National Energy Research Scientific Computing Center (NERSC), a federal supercomputing facility in California. But due to a backlog at NERSC, OCS’s role was key.

For the next analysis round the team is considering increasing the amount of work done through OSC. The survey will last five years, which means the need for high performance will increase.

The team built a powerful camera for the Blanco 4m telescope in order to collect the data. The key components of the 570-megapixel camera were built at Ohio State.

"We had to construct the most powerful instrument of its kind. It is sensitive enough to collect light from galaxies 8 billion light years away," said Honscheid.

It was easier to measure the structure of the universe in the past than it is to measure it is today. In the first 400,000 years after the Big Bang, the universe was filled with glowing gas and the light survives to this day. The cosmic microwave background (CMB) radiation provides an idea of the universe at the beginning. Since then, the gravity of dark matter has pulled mass together and made the universe clumpier. Dark energy has been fighting back and pushing matter apart. Using CBM as a start, cosmologists can calculate how the battle has played out over 14 billion years.

"With the new results, we are able for the first time to see the current structure of the universe with a similar level of clarity as we can see its infancy. Dark energy is needed to explain how the infant universe evolved to what we observe now," said MacCrann, a major contributor to the analysis.

DES scientist used two methods to measure the dark matter. They created maps of galaxy positions as tracers then they precisely measured the shapes of 26 million galaxies to directly map the patterns of dark matter over billions of light years, using a technique called gravitational lensing.

The DES team developed new ways to detect the tiny lensing distortions of galaxy images in order to make ultra-precise measurements. In the process, the researchers created the largest guide to spotting dark matter in the cosmos ever drawn. The new dark matter map is 10 times larger than the one DES released in 2015 and eventually will reach three times larger than it is now.

Michael Troxel, CCAPP postdoctoral fellow, and leader of the weak gravitational lensing analysis, added, "These results are based on unprecedented statistical power and detailed understanding of the telescope and potential biases in the analysis. Crucially, we performed a 'blind' analysis, in which we finalized all aspects of the analysis before we knew the results, thereby avoiding confirmation biases."

DES measurements of the present universe align with the results obtained by the Planck satellite that studies the cosmic microwave background radiation from when the universe was only 400,000 years old.

"The moment we realized that our measurement matched the Planck result within 7% was thrilling for the entire collaboration," said Honscheid. "And this is just the beginning for DES with more data already observed. With one more observing season to go, we expect to ultimately use five times more data to learn more about the enigmatic dark sector of the universe."

To read more about this study, visit the Dark Energy Survey site here.

To contact the author of this article, email Siobhan.Treacy@ieeeglobalspec.com


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