Researchers have developed the most detailed simulations yet of how matter accretes around black holes, incorporating full general relativity and radiation effects. Led by Lizhong Zhang from the Institute for Advanced Study and the Flatiron Institute, the study matches real astronomical observations. Published in The Astrophysical Journal, it focuses on stellar-mass black holes and uses powerful supercomputers.
Computational astrophysicists have made a significant advance in modeling black hole accretion, the process by which these cosmic objects draw in surrounding matter and release intense radiation. The new study, published in The Astrophysical Journal, introduces a computational framework that calculates matter flows into black holes without simplifying assumptions, fully accounting for Einstein's general relativity and radiation-dominated conditions.
Led by Lizhong Zhang, a joint postdoctoral research fellow at the Institute for Advanced Study's School of Natural Sciences and the Flatiron Institute's Center for Computational Astrophysics, the research began during Zhang's first year at the Institute in 2023-24 and continued at Flatiron. "This is the first time we've been able to see what happens when the most important physical processes in black hole accretion are included accurately," Zhang said. "These systems are extremely nonlinear -- any over-simplifying assumption can completely change the outcome. What's most exciting is that our simulations now reproduce remarkably consistent behaviors across black hole systems seen in the sky, from ultraluminous X-ray sources to X-ray binaries."
The models target stellar-mass black holes, which are about 10 times the mass of the Sun. Unlike supermassive black holes, these smaller objects evolve rapidly over minutes to hours, allowing real-time observations through spectral analysis of their emitted light. The simulations depict matter spiraling inward to form turbulent, glowing disks, along with outward-flowing winds and occasional jets.
To achieve this, the team accessed exascale supercomputers Frontier at Oak Ridge National Laboratory and Aurora at Argonne National Laboratory. Key contributions included radiation transport algorithms developed by Christopher White of Flatiron and Princeton University, and integration into the AthenaK code by Patrick Mullen, formerly at the Institute and now at Los Alamos National Laboratory.
Co-author James Stone, a professor at the Institute, highlighted the project's demands: "What makes this project unique is, on the one hand, the time and effort it has taken to develop the applied mathematics and software capable of modeling these complex systems, and, on the other hand, having a very large allocation on the world's largest supercomputers to perform these calculations. Now the task is to understand all the science that is coming out of it."
This first paper in a series paves the way for applying the framework to diverse black hole types, potentially illuminating supermassive ones that influence galaxy formation. The simulated spectra closely align with astronomical data, enhancing interpretations of these enigmatic objects.