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Peer-reviewedCC BY 4.0The Astrophysical Journal

Impact of Equation of State on Black Hole Accretion Flows and Radiative Properties

  • Yun-Ming Zhu1
  • Indu K. Dihingia1,2,3
  • Yosuke Mizuno1,4
  • Ziri Younsi5
  • Christian M. Fromm6,4
6 affiliations
  1. 1Shanghai Jiao-Tong University
  2. 2Ningbo University
  3. 3Zhejiang Key Laboratory of Extreme Universe
  4. 4Goethe-Universität
  5. 5University College London
  6. 6Universität Würzburg
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Abstract

Previous literature has documented that black hole shadow images are mainly shaped by spacetime geometry and plasma microphysics governing accretion flows. However, the influence of equations of state (EoS) remains underexplored. In this paper, we quantify how different plasma microphysics prescriptions, specifically the choice of EoS and electron-heating models, affect flow thermodynamics and the corresponding synthetic black hole images. We perform 3D general-relativistic magnetohydrodynamics (GRMHD) simulations using two constant- γ ideal EoSs with γ = 4/3 and 5/3 and a temperature-dependent variable EoS (TM) in both accretion flow states: Standard and Normal Evolution (SANE) and Magnetically Arrested Disk (MAD) regimes. The dynamical models are postprocessed with general-relativistic radiative transfer (GRRT) calculations at 86 and 230 GHz, employing thermal and hybrid κ electron distribution functions for synchrotron radiation. We also compare the two-temperature electron heating prescription based on turbulent heating and magnetic reconnection. The constant- γ EoSs systematically overestimate or underestimate gas and electron temperatures across disk and jet regions, whereas the variable EoS provides a smoother transrelativistic interpolation between the two limiting regimes. These differences substantively impact the synchrotron emissivity, image morphology, and the amplitude of flux variability. In particular, the variable EoS exhibits systematically larger temporal variability than the constant- γ models. These results demonstrate that adopting a physically self-consistent description of the EoS is essential for realistic modeling of accretion-flow thermodynamics and horizon-scale images like Event Horizon Telescope (EHT) observations.

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Cite

BibTeXRIS
BibTeX
@article{zhu2026impact,
  title = {{Impact of Equation of State on Black Hole Accretion Flows and Radiative Properties}},
  author = {Yun-Ming Zhu and Indu K. Dihingia and Yosuke Mizuno and Ziri Younsi and Christian M. Fromm},
  journal = {The Astrophysical Journal},
  year = {2026},
  month = oct,
  doi = {10.3847/1538-4357/aea8fd},
  url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea8fd},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Impact of Equation of State on Black Hole Accretion Flows and Radiative Properties
AU  - Yun-Ming Zhu
AU  - Indu K. Dihingia
AU  - Yosuke Mizuno
AU  - Ziri Younsi
AU  - Christian M. Fromm
PY  - 2026
DA  - 2026/10/14
JO  - The Astrophysical Journal
DO  - 10.3847/1538-4357/aea8fd
UR  - https://iopscience.iop.org/article/10.3847/1538-4357/aea8fd
AB  - Previous literature has documented that black hole shadow images are mainly shaped by spacetime geometry and plasma microphysics governing accretion flows. However, the influence of equations of state (EoS) remains underexplored. In this paper, we quantify how different plasma microphysics prescriptions, specifically the choice of EoS and electron-heating models, affect flow thermodynamics and the corresponding synthetic black hole images. We perform 3D general-relativistic magnetohydrodynamics (GRMHD) simulations using two constant- γ ideal EoSs with γ = 4/3 and 5/3 and a temperature-dependent variable EoS (TM) in both accretion flow states: Standard and Normal Evolution (SANE) and Magnetically Arrested Disk (MAD) regimes. The dynamical models are postprocessed with general-relativistic radiative transfer (GRRT) calculations at 86 and 230 GHz, employing thermal and hybrid κ electron distribution functions for synchrotron radiation. We also compare the two-temperature electron heating prescription based on turbulent heating and magnetic reconnection. The constant- γ EoSs systematically overestimate or underestimate gas and electron temperatures across disk and jet regions, whereas the variable EoS provides a smoother transrelativistic interpolation between the two limiting regimes. These differences substantively impact the synchrotron emissivity, image morphology, and the amplitude of flux variability. In particular, the variable EoS exhibits systematically larger temporal variability than the constant- γ models. These results demonstrate that adopting a physically self-consistent description of the EoS is essential for realistic modeling of accretion-flow thermodynamics and horizon-scale images like Event Horizon Telescope (EHT) observations.
SN  - 0004-637X
SN  - 1538-4357
ER  -