Scientists at the University of Chicago have used weak gravitational lensing to map dark matter and dark energy across a vast sky region, confirming the standard cosmological model. By analyzing archival telescope images, the team expanded galaxy shape measurements, resolving debates about cosmic structure growth. Their findings align observations of the nearby universe with early universe data from the cosmic microwave background.
In the standard Lambda-CDM model, dark matter and dark energy constitute about 95 percent of the universe, influencing galaxy formation and cosmic expansion without emitting light. Astrophysicists at the University of Chicago addressed this by studying subtle distortions in distant galaxy shapes caused by gravitational lensing, a phenomenon where mass bends light paths.
The Dark Energy Survey (DES), conducted from 2013 to 2019, used the Dark Energy Camera on the 4-meter Blanco Telescope at Chile's Cerro Tololo Inter-American Observatory to measure shapes of over 150 million galaxies across 5,000 square degrees of sky. Building on this, the Dark Energy Camera All Data Everywhere (DECADE) project incorporated additional archival images, nearly doubling the dataset to include shapes from more than 100 million galaxies over thousands of extra square degrees.
"Weak lensing measurements are best at probing the 'clumpiness' of matter," explained Dhayaa Anbajagane, a PhD student in Astronomy and Astrophysics and lead analyst on the DECADE papers. "Quantifying this clumpiness sheds light on the origin and evolution of structures like galaxies and galaxy clusters."
Distances to these galaxies were estimated via redshift, the shift of light to redder wavelengths indicating recession speed. Fitting the data to the Lambda-CDM model, which includes dark energy, dark matter, ordinary matter, neutrinos, and radiation, the results matched predictions for cosmic structure growth. Chihway Chang, associate professor of Astronomy and Astrophysics and DECADE lead, noted, "This is a well-tested model that has survived many, many examinations in the past decade, and our data point is going to add to that story."
Crucially, the findings showed no tension between weak lensing and cosmic microwave background observations, addressing a five-year debate. Combining DECADE with DES data created a catalog of 270 million galaxies spanning 13,000 square degrees—one-third of the sky—released to the scientific community this fall.
Alex Drlica-Wagner, a Fermilab scientist and UChicago associate professor who led DECADE observations, highlighted the project's innovation: "It was not clear that the DECADE dataset would be of sufficient quality to perform a cosmological analysis, but we have shown that it can indeed produce robust results."
This unconventional use of repurposed images, taken for diverse goals like studying dwarf galaxies or stars, demonstrates potential for future surveys such as the Vera C. Rubin Legacy Survey of Space and Time. The effort involved collaboration among UChicago, Fermilab, the National Center for Supercomputing Applications at the University of Illinois Urbana-Champaign, Argonne National Laboratory, the University of Wisconsin-Madison, and global partners. The results appear in the Open Journal of Astrophysics, with the primary paper detailing a new weak lensing shape catalog of 107 million galaxies.