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 on January 9 2019.

The survey is an international collaboration that began mapping a 5,000-square-degree area of the sky on Aug. 31, 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 4-meter 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.

According to DES Director Rich Kron, a Fermilab and University of Chicago scientist, those results and the scientists who made them possible are where much of the real accomplishment of DES lies.

“First generations of students and postdoctoral researchers on DES are now becoming faculty at research institutions and are involved in upcoming sky surveys,” Kron said. “The number of publications and people involved are a true testament to this experiment. Helping to launch so many careers has always been part of the plan, and it’s been very successful.”

Several members of staff and graduate students at the Institute of Astronomy (IoA) are part of the Dark Energy Survey Collaboration, and have been exploiting the new data from this experiment for a broad range of science. Dr. Manda Banerji and Prof. Richard McMahon are co-leads of the Galaxy and Quasars Science Working Group within DES. In a paper led by IoA graduate student, Clare Wethers, the Cambridge team used the deep images provided by DES to reveal, for the first time, lots of young stars forming in distant galaxies that contain powerful supermassive black-holes. Ordinarily the emission from a feeding black-hole or quasar is so bright that it dwarfs any emission from stars around it. “By looking at a special population of dust-enshrouded quasars where the light from the black-hole has been dimmed, we were able to exploit the unique sensitivity of DES to detect starlight in galaxies more than 10 billion light years away. This opens up a new observational window into our understanding of these mysterious and extreme, early galaxies” explains Dr. Banerji. 

Another discovery enabled by the data set is the detection of eleven new streams of stars around our Milky Way. Our home galaxy is surrounded by a massive halo of dark matter, which exerts a powerful gravitational pull on smaller, nearby galaxies. The Milky Way grows by pulling in, ripping apart and absorbing these smaller systems. As stars are torn away, they form streams across the sky that can be detected by the Dark Energy Survey.  Even so, stellar streams are extremely difficult to find since they are composed of relatively few stars spread out over a large area of sky.

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. IoA scientists continue to be involved in mining this truly astronomical dataset, and more new discoveries await.