Cosmologists have found new support for the Standard Cosmology Model through analysis of the structure of galaxy clusters. A recent study by a team of physicists from the US Department of Energy’s SLAC National Accelerator Laboratory and Stanford University made detailed measurements of the X-ray emission of galaxy clusters. These measurements revealed the internal distribution of matter in clusters and ultimately gave scientists the opportunity to examine the current dominant explanation for the structure and evolution of the universe, the lambda-CDM theory.

However, getting there was no easy task.

Here’s the problem: Understanding the mass distribution of galaxy clusters in terms of X-ray emissions is most reliable when the energy in the gas in the clusters is balanced by the gravitational force that holds the entire system together. Therefore, mass distribution measurements in real clusters focus on those that have entered a “relaxed” state. Therefore, it is important to take this loose set selection into account when comparing with theoretical predictions.

With this in mind, Elise Darragh-Ford, a graduate student in the Stanford Department of Physics, and her colleagues studied clusters created by computer simulations as part of the Three Hundred Project. First, they calculated what the X-ray emission should look like for each simulated cluster. They then applied the same observational criteria used to identify comfortable galaxy clusters from real data to the simulated images to eliminate the set.

Next, the researchers measured the relationship between three features — the cluster mass, how dense that mass is at the center, and the cluster redshift, which reflects how old the universe was when the light we observed was emitted — for both Project Three Hundred simulations. . Clusters and 44 real clusters observed by NASA’s Chandra X-ray Observatory.

The team found consistent results from both datasets: overall, clusters were more centrally concentrated over time, while at any given time, less large clusters were more centrally concentrated than larger ones. “The measured relationships fit very well between observation and theory and provide strong support for the Lambda-MCP paradigm,” said Darragh-Ford.

In the future, scientists hope to expand the size of both observed and simulated galaxy cluster datasets in their analysis. SLAC-supported projects that will be available online over the next few years, including the Rubin Observatory’s Ancient Space and Time Survey and the fourth-generation Cosmic Microwave Background (CMB-S4) experiment, will help identify even more galaxy clusters. Space missions such as the European Space Agency’s ATHENA satellite can perform X-ray measurements.

SLAC cosmologists are also working to expand the size and accuracy of computer simulations of the cosmos by making it possible to study galaxy clusters more thoroughly and to place tighter constraints on alternative cosmological scenarios.