Scientists from the University of Chicago have led a new study that maps large clusters of galaxies to help understand the fundamental laws of the universe. The research used data from the Dark Energy Survey, an initiative led by Fermi National Accelerator Laboratory, which observed the sky over six years from a site in Chile.
The team focused on galaxy clusters, some of the most massive objects in the universe. By analyzing how many there are and how they are distributed, researchers aim to test theories about how the universe formed and what rules govern it today.
Previous studies suggested there might be inconsistencies in current models of the universe, specifically the Lambda-CDM model. Some earlier findings indicated that the universe may have been more structured in the past than current models predict. This raised questions about whether updates to the Lambda-CDM model were needed.
However, the new analysis supports that the Lambda-CDM model remains a reliable explanation for what is observed. “Our results find that the Lambda-CDM model describes the observable universe well,” said Chun-Hao To, an Eric and Wendy Schmidt AI in Science Postdoctoral Fellow at UChicago and first author of one of the papers describing the analysis.
The research demonstrates that using galaxy clusters as a method to probe cosmological laws is valuable and sets a framework for future studies with upcoming telescopes. Chun-Hao To noted that this approach will be useful as more advanced observatories begin operations in coming years.
When looking at cosmic structures, galaxies tend to form groups or clusters. While our own group is relatively small with around 50 galaxies, other clusters are much larger and are among the most massive known objects. These massive structures can provide insights into dark matter and dark energy—forces that are not directly visible but influence how galaxies come together or move apart.
Because of their size, galaxy clusters are good candidates for observing these effects. Early studies faced challenges because some clusters might be hidden behind others, affecting calculations. “Because clusters are such a sensitive measuring stick, if we tallied less clusters, for example, we would conclude a different amount of dark matter in the universe,” said Chihway Chang, senior author and associate professor of astronomy and astrophysics at UChicago.
Chang and To explained that their study accounts for these complications. Their findings also contribute to an ongoing discussion among cosmologists known as the “S8 tension.” S8 measures how much structure exists in the universe. Earlier studies using weak gravitational lensing suggested a slightly lower S8 value compared to predictions based on data from the early universe.
If confirmed, this discrepancy could indicate gaps in understanding within the Lambda-CDM model. But according to this new study using galaxy cluster data, S8 aligns with earlier measurements from the early universe. “This approach of using galaxy clusters as a test of big cosmological questions is somewhat independent from other measurements,” Chang said. Consistent results across different methods increase confidence in scientific conclusions.
With new telescopes like the Rubin Observatory Legacy Survey of Space and Time and the Nancy Grace Roman Space Telescope set to become operational soon, researchers expect to map even more galaxy clusters and gather additional information. “We’re glad to demonstrate an analysis scheme that provides us with a different angle on the universe,” said To.
The research included 66 members of the Dark Energy Survey Collaboration from over 50 institutions worldwide, including Argonne National Laboratory and Fermilab—both affiliated with UChicago. Part of the work was done at UChicago’s Research Computing Center.
“This approach of using galaxy clusters as a test of big cosmological questions is somewhat independent from other measurements,” Chang explained. That’s important to scientists—if they see the same result using different approaches, it makes that conclusion more likely to be true.
“We’re glad to demonstrate an analysis scheme that provides us with a different angle on the universe,” said To.