Jet Formation in 3D GRMHD Simulations of Bondi–Hoyle–Lyttleton Accretion

Abstract

A black hole (BH) traveling through a uniform, gaseous medium is described by Bondi–Hoyle–Lyttleton (BHL) accretion. If the medium is magnetized, then the black hole can produce relativistic outflows. We performed the first 3D, general-relativistic magnetohydrodynamic simulations of BHL accretion onto rapidly rotating black holes using the H-AMR code, where we mainly varied the strength of a background magnetic field that threads the medium. We found that the ensuing accretion continuously drags the magnetic flux to the BH, which accumulates near the event horizon until it becomes dynamically important. Depending on the strength of the background magnetic field, the BHs can sometimes launch relativistic jets with high enough power to drill out of the inner accretion flow, become bent by the headwind, and escape to large distances. For stronger background magnetic fields, the jets are continuously powered, while at weaker field strengths they are intermittent, turning on and off depending on the fluctuating gas and magnetic flux distributions near the event horizon. We find that our jets reach extremely high efficiencies of ∼100%–300%, even in the absence of an accretion disk. We also calculated the drag forces exerted by the gas onto to the BH and found that the presence of magnetic fields causes the drag forces to be much less efficient than in unmagnetized BHL accretion. They can even sometimes become negative, accelerating the BH rather than slowing it down. Our results extend classical BHL accretion to rotating BHs moving through magnetized media, and demonstrate that accretion and drag are significantly altered in this environment.

Hydrodynamics and Survivability during Post-main-sequence Planetary Engulfment

“…R a , the material in front of the SB dominates gravitational drag (as opposed to material behind the SB, as when R SB = R a ), and the gravitational drag coefficient becomes negative. Similar results have been found for compact objects with outflows (Gruzinov et al 2020;Li et al 2020;Kaaz et al 2023) and luminous planetesimals moving through a disk (Masset & Velasco Romero 2017;Masset 2017). In those settings, feedback from the object can interfere with the flow at impact parameters ∼R a that the SB would have gravitationally focused had there been no feedback.…”

Electromagnetic Counterparts Powered by Kicked Remnants of Black Hole Binary Mergers in AGN Disks

“…The hyper-Eddington accretion is realizable, since for BHL accretion the inflow is highly quasispherical (e.g., El Mellah & Casse 2015) and the released gravitational energy is advected inward with gas (Begelman 1979). Meanwhile, the AGN disk would be magnetized, with a ratio of ambient gas to magnetic pressure β  10-100 (King et al 2007;Salvesen et al 2016;Kaaz et al 2023a). Recent numerical simulations indicate that the ambient magnetic fields are frozen and flow inward with gas, resulting in their accumulation to saturation near the BH (Kaaz et al 2023a;Kwan et al 2023).…”

“…Meanwhile, the AGN disk would be magnetized, with a ratio of ambient gas to magnetic pressure β  10-100 (King et al 2007;Salvesen et al 2016;Kaaz et al 2023a). Recent numerical simulations indicate that the ambient magnetic fields are frozen and flow inward with gas, resulting in their accumulation to saturation near the BH (Kaaz et al 2023a;Kwan et al 2023). Due to a large spin of the merger remnant (e.g., Tichy & Marronetti 2008;, a jet would be generated via the Blandford-Znajek (BZ) mechanism (Blandford & Znajek 1977), the power of which can be estimated as…”

“…where f ∼ 0.1 for β  10-100 (according to Figure 3 in Kaaz et al 2023a), which contains the effects of both the jet efficiency and the reduction in accretion rate.…”

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

“…Recently, some attempts to connect these disparate scales have been made using nested simulations where each smallerscale simulation is initialized from the next larger-scale simulation (e.g., Hopkins & Quataert 2010;Ressler et al 2020;Guo et al 2023), or by adopting Lagrangian hyperrefinement methods (e.g., Anglés-Alcázar et al 2021;Hopkins et al 2023), or by pushing out the simulation regime to larger scales (e.g., Lalakos et al 2022;Kaaz et al 2023). While successful in studying the process of accretion, feedback from the SMBH has not been followed out to galaxy scales in prior work because either the communication between scales is only directed inward or because of the inability to include the entire galaxy and the black hole.…”