Bridging Scales in Black Hole Accretion and Feedback: Magnetized Bondi Accretion in 3D GRMHD

Abstract

Fueling and feedback couple supermassive black holes (SMBHs) to their host galaxies across many orders of magnitude in spatial and temporal scales, making this problem notoriously challenging to simulate. We use a multi-zone computational method based on the general relativistic magnetohydrodynamic (GRMHD) code KHARMA that allows us to span 7 orders of magnitude in spatial scale, to simulate accretion onto a non-spinning SMBH from an external medium with a Bondi radius of R B ≈ 2 × 105 GM •/c 2, where M • is the SMBH mass. For the classic idealized Bondi problem, spherical gas accretion without magnetic fields, our simulation results agree very well with the general relativistic analytic solution. Meanwhile, when the accreting gas is magnetized, the SMBH magnetosphere becomes saturated with a strong magnetic field. The density profile varies as ∼r −1 rather than r −3/2 and the accretion rate M ̇ is consequently suppressed by over 2 orders of magnitude below the Bondi rate M ̇ B . We find continuous energy feedback from the accretion flow to the external medium at a level of ∼ 10 − 2 M ̇ c 2 ∼ 5 × 10 − 5 M ̇ B c 2 . Energy transport across these widely disparate scales occurs via turbulent convection triggered by magnetic field reconnection near the SMBH. Thus, strong magnetic fields that accumulate on horizon scales transform the flow dynamics far from the SMBH and naturally explain observed extremely low accretion rates compared to the Bondi rate, as well as at least part of the energy feedback.

Black Hole–Disk Interactions in Magnetically Arrested Active Galactic Nuclei: General Relativistic Magnetohydrodynamic Simulations Using a Time-dependent, Binary Metric

“…This is not only because avoiding numerical relativity makes the computation faster, but it will allow the community to take full advantage of the numerous advances made in single black hole GRMHD codes if these are adapted for time-dependent metrics. For instance, in the past couple of decades, the GRMHD accretion community has been able to explore effects such as varying black hole spin (Event Horizon Telescope Collaboration et al 2019;Akiyama et al 2022), varying magnetic flux supply (Tchekhovskoy et al 2011;Narayan et al 2012), varying disk tilt (McKinney et al 2013;Liska et al 2018;White et al 2019a;Chatterjee et al 2020), including radiative effects (Ryan et al 2015;White et al 2023), including nonideal physics (Ressler et al 2015;Chandra et al 2017;Foucart et al 2017;Ripperda et al 2019), and studying a variety of initial conditions informed by larger scales (Ressler et al 2020b(Ressler et al , 2021Cho et al 2023;Kaaz et al 2023;Lalakos et al 2024). Furthermore, since the user base for GRMHD is currently much larger than that for numerical relativity (e.g., Porth et al 2019), it could encourage more researchers to study binary black hole systems.…”