Dark Energy Survey releases catalog of nearly 700 million astronomical objects to the public

Pioneering Fermilab-led survey covered 5,000 square degrees of the southern sky

The Dark Energy Survey is releasing to the public a massive collection of astronomical data and calibrated images collected over six years of scanning the southern skies. The release, which includes images of nearly 700 million astronomical objects, is one of the largest astronomical catalogs issued to date.

The Dark Energy Survey, or DES, was an international collaboration led by UChicago-affiliated Fermi National Accelerator Laboratory, which spent more than half a decade collecting and analyzing data from the sky. The project covered 5,000 square degrees of the southern sky (one-eighth of the entire sky) and spanning billions of light-years, with the ultimate goal of understanding the accelerating expansion of the universe and the phenomenon called “dark energy” thought to be responsible for this expansion. 

The new catalog, called DR2, was released by a collaboration including Fermilab, the University of Illinois at Champaign-Urbana’s National Center for Supercomputing Applications, and the National Science Foundation’s NOIRLab, during a session held Jan. 14 at the 237th Meeting of the American Astronomical Society. 

“This is a momentous milestone. For six years, the Dark Energy Survey collaboration took pictures of distant celestial objects in the night sky. Now, after carefully checking the quality and calibration of the images captured by the Dark Energy Camera, we are releasing this second batch of data to the public,” said Dark Energy Survey director Rich Kron, Prof. Emeritus of Astronomy & Astrophysics at the University of Chicago and Fermilab scientist. “We invite professional and amateur scientists alike to dig into what we consider a rich mine of gems waiting to be discovered.”

DR2 is the second data release in the survey’s seven-year history, building on the 400 million objects cataloged with the survey’s prior data release and improving on it by refining calibration techniques. Paired with the deeper combined images, DR2 includes improved estimates of the amount and distribution of matter in the universe.

Astronomical researchers around the world can access these unprecedented data and mine them to make new discoveries about the universe, complementary to the studies being carried out by the Dark Energy Survey collaboration. The full data release is online and available to the public to explore.

Cosmic controversies

The Dark Energy Survey was designed to map hundreds of millions of galaxies and to discover thousands of supernovae in order to measure the history of cosmic expansion and the growth of large-scale structure in the universe, both of which reflect the nature and amount of dark energy in the universe. The primary tool in collecting these images, the Dark Energy Camera, is mounted to the Víctor M. Blanco 4-meter Telescope, part of the Cerro Tololo Inter-American Observatory in the Chilean Andes, part of National Science Foundation’s NOIRLab

Previously the Dark Energy Survey produced the largest and most accurate dark matter map from galaxy weak lensing to date; a new map, three times larger, will be released in the near future. 

But the survey data also enables many other investigations covering a vast range of cosmic distances—from discovering new nearby solar system objects to investigating the nature of the first star-forming galaxies in the early universe. 

For example, one early result relates to the construction of a catalog of a type of pulsating star known as “RR Lyrae,” which tells scientists about the region of outer space beyond the edge of our Milky Way. In this area nearly devoid of stars, the motion of the RR Lyrae hint at the presence of an enormous “halo” of invisible dark matter, which may provide clues on how our galaxy was assembled over the last 12 billion years. 

In another result, scientists used the extensive DR2 galaxy catalog, along with data from the LIGO experiment, to estimate the location of a black hole merger and, independent of other techniques, infer the value of the Hubble constant, a key cosmological parameter. 

Combining their data with other surveys, DES scientists have also been able to generate a complete map of Milky Way’s dwarf satellites, giving researchers insight into how our own galaxy was assembled and how it compares with cosmologists’ predictions. The detailed precision cosmology constraints based on the full six-year DES data set will come out over the next two years.

Still processing

Even though the sky mapping concluded in 2019, it will take years to analyze the data.

How it works: The Dark Energy Camera images (and the large amount of data surrounding them) are transferred to the National Center for Supercomputing Applications for processing via the DES Data Management project. Using the Blue Waters supercomputer at NCSA, the Illinois Campus Cluster, and compute systems at Fermilab, NCSA prepares calibrated data products for public and research consumption. It takes approximately four months to process one year’s worth of data into a searchable, usable catalog.

The DES DR2 is hosted at the Community Science and Data Center, a program of the National Science Foundation’s NOIRLab. CSDC provides software systems, user services and development initiatives to connect and support the scientific missions of NOIRLab’s telescopes, including the Blanco Telescope at Cerro Tololo Inter-American Observatory. NCSA, NOIRLab and the LIneA Science Server collectively provide the tools and interfaces that enable access to DR2.

“With information on the positions, shapes, sizes, colors and brightnesses of over 690 million stars, galaxies and quasars, the release promises to be a valuable source for astronomers and scientists worldwide to continue their explorations of the universe, including studies of matter (light and dark) surrounding our home Milky Way Galaxy, as well as pushing further to examine groups and clusters of distant galaxies, which hold precise evidence about how the size of the expanding universe changes over time,” said Dark Energy Survey data management project scientist Brian Yanny of Fermilab.

The Dark Energy Survey is a collaboration of more than 400 scientists from 26 institutions in seven countries. The full list of collaborating institutions in the Dark Energy Survey can be found at www.darkenergysurvey.org/collaboration

Funding: U.S. Department of Energy Office of Science, U.S. National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, Funding Authority for Funding and Projects in Brazil, Carlos Chagas Filho Foundation for Research Support of the State of Rio de Janeiro, Brazilian National Council for Scientific and Technological Development and the Ministry of Science and Technology, the German Research Foundation

Adapted from an article by Leah Hesla that first appeared on the Fermilab website.