Dark Energy Survey completes six-year mission

After scanning in depth about a quarter of the southern skies for six years and cataloguing hundreds of millions of distant galaxies, the Dark Energy Survey (DES) will finish taking data tomorrow, on 9 January.

The Blanco telescope at Cerro Tololo

The survey is an international collaboration, of which the University of Portsmouth is a founding member, that began mapping a 5,000-square-degree area of the sky on 31 August 2013, in a quest to understand the nature of dark energy, the mysterious force that is accelerating the expansion of the universe.

Using the Dark Energy Camera, a 520-megapixel digital camera funded by the U.S. Department of Energy Office of Science and mounted on the Blanco four-metre telescope at the National Science Foundation’s Cerro Tololo Inter-American Observatory in Chile, scientists on DES took data on 758 nights over six years.

Over those nights, they recorded data from more than 300 million distant galaxies. More than 400 scientists from over 25 institutions around the world have been involved in the project, which is hosted by the U.S. Department of Energy’s Fermi National Accelerator Laboratory. The collaboration has already produced about 200 academic papers, with more to come.

Professor David Bacon from the University’s Institute of Cosmology and Gravitation,  is a member of the DES. He said: “The Dark Energy Survey has been an incredible project so far, bringing us important information about the expansion and structure of the Universe. We can’t wait to dive deeper into the complete dataset to make further discoveries.”

DES remains one of the most sensitive and comprehensive surveys of distant galaxies ever performed. The Dark Energy Camera is capable of seeing light from galaxies billions of light-years away and capturing it in unprecedented quality.

According to Alistair Walker of the National Optical Astronomy Observatory, a DES team member and the DECam instrument scientist, equipping the telescope with the Dark Energy Camera transformed it into a state-of-the-art survey machine.

“DECam was needed to carry out DES, but it also created a new tool for discovery, from the solar system to the distant universe,” Walker said. “For example, 12 new moons of Jupiter were recently discovered with DECam (https://phys.org/news/2018-07-jupiter-moon-tiny-oddball.html), and the detection of distant star-forming galaxies in the early universe, when the universe was only a few percent of its present age, has yielded new insights into the end of the cosmic dark ages (https://www.noao.edu/news/2017/pr1703.php).”

The Dark Energy Camera

The survey generated 50 terabytes (that’s 50 million megabytes) of data over its six observation seasons. That data is stored and analysed at the National Center for Supercomputing Applications (NCSA) at the University of Illinois at Urbana-Champaign.

Now the job of analysing that data takes centre stage. DES has already released a full range of papers based on its first year of data, and scientists are now diving into the rich seam of catalogued images from the first several years of data, looking for clues to the nature of dark energy.

Scientific highlights from previous years include:

DES scientists also spotted the first visible counterpart of gravitational waves ever detected, a collision of two neutron stars that occurred 130 million years ago. (http://news.fnal.gov/2017/10/scientists-spot-explosive-counterpart-ligovirgos-latest-gravitational-waves) DES was one of several sky surveys that detected this gravitational wave source, opening the door to a new kind of astronomy.

The Dark Energy Camera will remain mounted on the Blanco telescope at Cerro Tololo for another five to 10 years and will continue to be a useful instrument for scientific collaborations around the world.

The DES collaboration will now focus on generating new results from its six years of data, including new insights into dark energy. With one era at an end, the next era of the Dark Energy Survey is just beginning.

Follow the Dark Energy Survey online at www.darkenergysurvey.org and connect with the survey on Facebook at www.facebook.com/darkenergysurvey, on Twitter at www.twitter.com/theDESurvey and on Instagram at www.instagram.com/darkenergysurvey.

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