Abstract
Accreting supermassive black hole binaries are powerful multimessenger sources emitting both gravitational and electromagnetic (EM) radiation. Understanding the accretion dynamics of these systems and predicting their distinctive EM signals is crucial to informing and guiding upcoming efforts aimed at detecting gravitational waves produced by these binaries. To this end, accurate numerical modeling is required to describe both the spacetime and the magnetized gas around the black holes. In this paper, we present two key advances in this field of research. First, we have developed a novel 3D general relativistic magnetohydrodynamics (GRMHD) framework that combines multiple numerical codes to simulate the inspiral and merger of supermassive black hole binaries starting from realistic initial data and running all the way through merger. Throughout the evolution, we adopt a simple but functional prescription to account for gas cooling through photon emission. Next, we have applied our new computational method to follow the time evolution of a circular, equal-mass, nonspinning black hole binary for ~200 orbits, starting from a separation of 20rg and reaching the postmerger evolutionary stage of the system. We have shown how mass continues to flow toward the binary even after the binary “decouples” from its surrounding disk, but the accretion rate onto the black holes diminishes. We have identified how the minidisks orbiting each black hole are slowly drained and eventually dissolve as the binary compresses. We confirm previous findings that the system’s luminosity decreases by a factor of a few during inspiral; however, we observe an abrupt increase by ~50% in this quantity at the time of merger, likely accompanied by an equally abrupt change in spectrum. Finally, we have demonstrated that during the inspiral, fluid ram pressure regulates the fraction of the magnetic flux transported to the binary that attaches to the black holes’ horizons.
| Original language | English |
|---|---|
| Pages (from-to) | 063009-1-063009-36 |
| Journal | Physical Review D |
| Volume | 112 |
| Issue number | 6 |
| DOIs | |
| State | Published - Sep 4 2025 |
Funding
The authors would like to thank the anonymous referee for a thorough reading of the manuscript and insightful comments and suggestions. We would also like to thank Zachariah B. Etienne and Carlos Lousto for insightful physics-related discussions and Steve Fromm for a careful reading of the manuscript.We also appreciate the assistance of Roland Haas in helping us modify his ReadInterpolate code for our purposes. The authors gratefully acknowledge the National Science Foundation (NSF) for financial support from Grants No. AST-2009260, No. AST-2009330, No. PHY-2409706, No. PHY-2110338, No. PHY- 2110339, and No. OAC-2004044, as well as the National Aeronautics and Space Administration (NASA) for financial support from TCAN Grant No. 80NSSC24K0100. Work at Oak Ridge National Laboratory is supported under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy (DOE). V. M. was also supported by the Exascale Computing Project (17-SC-20-SC), a collaborative effort of the DOE Office of Science and the National Nuclear Security Administration. This research used resources from the Texas Advanced Computing Center’s (TACC) Frontera and Vista supercomputer allocations (Award No. PHY20010). Additional resources were provided by the BlueSky, Green Prairies, and Lagoon clusters of the Rochester Institute of Technology (RIT) acquired with NSF Grants No. PHY- 2018420, No. PHY-0722703, No. PHY-1229173, and No. PHY-1726215. This manuscript has been authored by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy (DOE).