# Relativistic Gas Accretion onto Supermassive Black Hole Binaries from Inspiral through Merger

**Authors:** Lorenzo Ennoggi, Manuela Campanelli, Yosef Zlochower, Scott C. Noble, Julian Krolik, Federico Cattorini, Jay V. Kalinani, Vassilios Mewes, Michail Chabanov, Liwei Ji, Maria Chiara de Simone  
**arXiv:** [2502.06389](https://arxiv.org/abs/2502.06389)  
**Date:** 2025-02-10  
**Summary page:** https://www.summarizepaper.com/en/paper/2502.06389v1/

## Key points

- Accreting supermassive black hole binaries are powerful multimessenger sources emitting gravitational and electromagnetic radiation.
- Accurate modeling of these systems is crucial for predicting their electromagnetic signals and detecting gravitational waves.
- Researchers developed a novel 3D general relativistic magnetohydrodynamics (GRMHD) framework to simulate the inspiral and merger of supermassive black hole binaries.
- Computational method tracked the evolution of a circular, equal-mass, non-spinning black hole binary for approximately 200 orbits from a separation of 20 gravitational radii.
- Study identified how minidisks dissolve as the binary compresses and showed an increase in luminosity by around 50% at the time of merger with a significant change in spectrum.
- Magnetic flux brought to the spin-parameter merger remnant can drive a relativistic, Poynting-flux-dominated jet.
- Research utilized resources from Texas Advanced Computing Center's Frontera and Vista supercomputer allocations, as well as clusters at Rochester Institute of Technology acquired through NSF grants.
- Two codes—CactusSurfaceIntegrals and CactusVolumeIntegrals—were developed to calculate integrals over surfaces and volumes for physical insights gained from simulations.

## Summary

In this study, the focus is on accreting supermassive black hole binaries as powerful multimessenger sources emitting both gravitational and electromagnetic radiation. The accurate modeling of these systems is crucial for predicting their electromagnetic signals and detecting gravitational waves produced by these binaries. To address this, the researchers 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 from realistic initial data through to post-merger stages. The computational method was applied to track the evolution of a circular, equal-mass, non-spinning black hole binary for approximately 200 orbits, starting from a separation of 20 gravitational radii. The study identified how minidisks dissolve as the binary compresses and showed that even when the binary separates from its surrounding disk, its luminosity only decreases slightly before abruptly increasing by around 50% at the time of merger. This increase in luminosity is accompanied by a significant change in spectrum. Furthermore, it was observed that the magnetic flux brought to the spin-parameter merger remnant can drive a relativistic, Poynting-flux-dominated jet. The research utilized resources from Texas Advanced Computing Center's Frontera and Vista supercomputer allocations, as well as clusters at Rochester Institute of Technology acquired through NSF grants. To analyze the physical insights gained from the simulation, two codes—CactusSurfaceIntegrals and CactusVolumeIntegrals—were developed to calculate integrals over surfaces and volumes. These codes allow for integration of various quantities of interest over planar, spherical, or cylindrical surfaces embedded in Cactus grids with Cartesian topology and box-in-box mesh refinement. The workflow involves assigning MPI tasks to surface chunks and determining grid components with fine resolution overlapping each point on the surface chunk. Overall, this research provides valuable insights into accreting supermassive black hole binaries' dynamics and emission properties through advanced numerical modeling techniques and analysis tools developed specifically for this purpose.