# Hot, cold, and multi-component accretion flows around supermassive black hole binaries

**Authors:** Christopher Tiede, Daniel J. D'Orazio  
**arXiv:** [2508.11748](https://arxiv.org/abs/2508.11748)  
**Date:** 2025-08-15  
**Summary page:** https://www.summarizepaper.com/en/paper/2508.11748v1/

## Key points

- Comprehensive model for studying supermassive black hole binaries (SMBHBs) accreting below Eddington limit
- Focus on systems with hot, advection-dominated flows
- Analysis of spectral characteristics of multi-component accretion flows transitioning between cold, thin disks and hot torii based on local accretion rate
- Findings suggest binary accretion processes can explain features observed in standard active galactic nuclei (AGN)
- Identification of hydrodynamic modulation at binary period in thermal emission and low-frequency synchrotron components
- Application of model to SMBHB candidate PG1302-102 with mixed-component accretion state and jet feature accurately reproducing observed broadband spectrum
- Framework aids in interpreting candidate SMBHBs and motivates future multi-wavelength investigations of potential multi-messenger sources
- Conclusion outlines avenues for further research and development in understanding multi-component binary accretion flows and their implications for astrophysical phenomena involving supermassive black holes

## Summary

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The authors present a comprehensive model for studying supermassive black hole binaries (SMBHBs) accreting below their Eddington limit. The focus is on systems where hot, advection-dominated flows are feasible. The study delves into the spectral characteristics of multi-component accretion flows that can transition between cold, thin disks and hot, advection-dominated torii based on the local accretion rate. By employing a three-disk model, the researchers calculate spectral energy distributions for four distinct accretion configurations and analyze their observational implications, including potential variability at the binary orbital period. The findings suggest that binary accretion processes can effectively explain many features observed in standard active galactic nuclei (AGN). The analysis of variability indicates that hydrodynamic modulation at the binary period is most prominent in thermal emission and low-frequency synchrotron components. Additionally, periodic variability induced by Doppler boosting of emitting material bound to a single binary component is identified. The model is applied to the SMBHB candidate PG1302-102, demonstrating that a mixed-component accretion state combined with a jet feature can accurately reproduce the observed broadband spectrum. This framework not only aids in interpreting candidate SMBHBs but also motivates future multi-wavelength investigations of potential multi-messenger sources. The study concludes by outlining avenues for further research and development in understanding multi-component binary accretion flows and their implications for astrophysical phenomena involving supermassive black holes.