SUNY Polytechnic Institute (SUNY Poly) Assistant Professor of Physics, Dr. Shing-Chi Leung, together with collaborators Dr. Ken’ichi Nomoto, Professor Emeritus at the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) at The University of Tokyo, and Dr. Aurora Simionescu, Senior Scientist at the Netherlands Institute for Space Research (SRON), published an article in The Astrophysical Journal titled “Revisiting the Perseus Cluster I: Resolving the Si/S/Ar/Ca Ratios by Stellar Convection” (ApJ 990, 207, 2025). 

The Perseus Cluster is one of the largest known structures in the universe. Located in the direction of the Perseus Constellation, it contains over a thousand galaxies with a combined mass about a thousand trillion times greater than the Sun. The space between its galaxies—called the intracluster medium (ICM)—is filled with extremely hot gas. This gas glows in X-rays, which telescopes can detect, and it contains the chemical fingerprints of billions of supernova explosions that have happened across cosmic history.

The Hitomi telescope (Astro-H), before it broke apart in 2018, measured the X-ray spectrum of this hot gas with great precision. Surprisingly, the chemical makeup looked very similar to that of the Sun. However, existing models could not explain this pattern. They predicted too much silicon and sulfur, and not enough argon and calcium—elements typically made in abundance by very massive stars (those at least ten times heavier than the Sun). This mismatch suggested a deeper problem in how scientists model these stars.

The team discovered how stellar convection (the movement of hot material inside stars) is represented in simulations plays a major role. A key number, known as the “mixing length parameter,” determines how strongly convection is modeled. But this number has been uncertain, with different calibrations depending on the type of star. To resolve this, Dr. Leung and colleagues tested different values in detailed stellar evolution models to see which best matched the observations. They found that a higher value of 2.2 worked well, consistent with other measurements from nearby stars such as Betelgeuse.

“The main takeaway is twofold,” explained Dr. Leung. “First, our new models show how massive stars typically explode, and what the results look like when billions of them enrich their surroundings. Second, differences in this convection parameter suggest that convection—a process we see every day, like boiling water—is much more subtle and fascinating than we might think.”

The team’s next step is to expand their models to include massive stars from different stages of the universe’s history, in order to better explain how generations of stars contributed to the Perseus Cluster’s chemical makeup.

This project is supported by the National Science Foundation under grant AST-2316807.