The Large Synoptic Survey Telescope (LSST) rests atop El Peñón, an 8,800-foot mountain peak along the Cerro Pachón ridge among the foothills of the Andes in northern Chile. It keeps good company with the closely situated Gemini Observatory-South and the Southern Astrophysical Research Telescope.
A partnership between the U.S. Department of Energy’s (DOE) Office of Science and the National Science Foundation (NSF), the LSST is among a new generation of ground-based telescopes supported by advanced supercomputing and data analysis tools, some of them provided by DOE’s Argonne National Laboratory.
Scheduled to begin its observations in 2021, the LSST’s 8.4-meter (27.6-foot) primary mirror, coupled with the world’s largest digital camera, will capture a continuous stream of images and generate massive datasets of roughly half the visible sky every night.
To prepare for this flood of data, an ambitious campaign is underway to create simulated LSST data that will test image analysis techniques and ensure that analysis on actual images is accurate, opening the door to pivotal discoveries of the cosmos.
Perhaps, from within the analyses results will emerge the clues to solving the enigma of dark energy and its relationship to the accelerated expansion of the universe, a riddle that has confounded science for nearly a century.
Believed to comprise roughly 70 percent of the universe, dark energy and its role in cosmic expansion form one of five interconnected areas of science supported by the Office of High Energy Physics within DOE’s Office of Science.
The LSST’s mission to unlock the mystery falls to its Dark Energy Science Collaboration (DESC), an international collaboration of more than 800 members, many from DOE facilities like Argonne, Brookhaven National Laboratory, Lawrence Berkeley National Laboratory, SLAC National Accelerator Laboratory and Fermilab.
Shedding light on dark energy
“We already know that understanding dark energy will be very difficult,” said Katrin Heitmann, Argonne physicist and computational scientist and Computing and Simulation Coordinator for the DESC. “But the results of this research could shed new light on the physical nature of dark energy and further our understanding of the universe and its evolution.”
The picture is not entirely clear, but there is very strong evidence that galaxies are intimately bound to large clumps of dark matter, an unidentified form of matter five times more abundant than the visible matter in the universe. The dark matter distribution, initially very smooth, forms a complex web-like structure made of dark matter concentrations — non-luminous “halos” — in which galaxies are eventually formed. Understanding the distribution and its evolution may one day inform our understanding of dark energy.
“By applying this knowledge of dark matter and galaxies together, we can create a powerful tool to probe how the universe evolves over time and get a sense for how dark energy might fit into current cosmological models,” said Antonio Villarreal, a postdoctoral appointee at Argonne’s Leadership Computing Facility (ALCF), a DOE Office of Science User Facility.
He and more than 50 researchers from the DESC’s computing and analysis working groups are running a dress rehearsal of sorts to ready the stage for such discovery. Their set, a massive simulation intended to accurately reflect data generated by the LSST; the props and scenery guided by the composition of galaxies and optical effects created by the atmosphere, the Milky Way, even the telescope itself.
The first scene opens on the “Outer Rim.”
A key player in this scenario, Heitmann was among a cohort of researchers utilizing the ALCF to produce the “Outer Rim” simulation, among the largest high-resolution simulations of the universe in the world. A cosmological canvas on which to describe galaxy models, the Outer Rim simulation tracks the distribution of matter in the universe as governed by the fundamental principles of physics, as well as input from earlier sky surveys.