UChicago Scientists Map Galaxy Clusters to Unlock Universe’s Secrets

A team of scientists from the University of Chicago has unveiled a study that maps some of the largest known structures in the universe, offering new insights into fundamental questions about its formation and governing principles. The research, released on October 21, 2023, utilizes data from the Dark Energy Survey, a major initiative managed by the U.S. Department of Energy’s Fermilab. Over six years, this project meticulously catalogued celestial phenomena from a mountaintop in Chile.

Using this extensive dataset, the researchers focused on galaxy clusters, which can be thought of as neighborhoods in the cosmos. Just as a home on Blackstone Avenue is part of the larger community in Hyde Park, the Earth resides in a spiral arm of the Milky Way Galaxy, which occupies a region with around 50 other galaxies. These clusters vary in size, with some being among the most massive objects known to science.

The primary goal of the study was to investigate the nature of dark matter and dark energy—two mysterious forces that influence the behavior of galaxies. Dark matter, which cannot be directly observed, pulls galaxies together, while dark energy pushes them apart. The immense mass of galaxy clusters makes them ideal for examining the effects of these forces, providing clearer insights than smaller celestial bodies could.

Challenges have arisen in previous studies where galaxy clusters were obscured from view, resulting in inaccurate calculations of their properties. Chihway Chang, a senior author of the study and associate professor of astronomy and astrophysics at the University of Chicago, noted, “Because clusters are such a sensitive measuring stick, if we tallied fewer clusters, we would conclude a different amount of dark matter in the universe.”

Despite these hurdles, Chang and co-author Chun-Hao To, a postdoctoral fellow at the University of Chicago, developed methods to overcome the obstacles and enhance their analysis. Their research introduced a new metric known as “S8 tension,” which quantifies the clumpiness of the universe or its overall structure.

Past studies using alternative techniques suggested that the S8 value was slightly lower than what could be inferred from the early universe. If this were accurate, it would imply that the universe had developed more structure in its earlier stages than it does today, potentially undermining the ICDM model, the prevailing theoretical framework that describes the universe in terms of dark energy and cold dark matter.

In contrast, the current analysis of galaxy clusters indicates that today’s S8 value aligns with that of the early universe, thereby supporting the integrity of the ICDM model.

Looking ahead, the next generation of large telescopes is anticipated to significantly broaden the scope of galaxy cluster mapping, providing even more opportunities for groundbreaking research. The study involved 66 experts from the Dark Energy Survey Collaboration, representing over 50 institutions, including Fermilab and the Argonne National Laboratory.

This research not only advances our understanding of the universe but also reinforces the collaborative efforts within the scientific community to tackle some of the most profound questions regarding our cosmic environment.