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ABSTRACT We present 3D general relativistic magnetohydrodynamic simulations of zero angular momentum accretion around a rapidly rotating black hole, modified by the presence of initially uniform magnetic fields. We consider several angles between the magnetic field direction and the black hole spin. In the resulting flows, the mid-plane dynamics are governed by magnetic reconnection-driven turbulence in a magnetically arrested (or a nearly arrested) state. Electromagnetic jets with outflow efficiencies ∼10–200 per cent occupy the polar regions, reaching several hundred gravitational radii before they dissipate due to the kink instability. The jet directions fluctuate in time and can be tilted by as much as ∼30○ with respect to black hole spin, but this tilt does not depend strongly on the tilt of the initial magnetic field. A jet forms even when there is no initial net vertical magnetic flux since turbulent, horizon-scale fluctuations can generate a net vertical field locally. Peak jet power is obtained for an initial magnetic field tilted by 40○–80○ with respect to the black hole spin because this maximizes the amount of magnetic flux that can reach the black hole. These simulations may be a reasonable model for low luminosity black hole accretion flows such as Sgr A* or M87.
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Dual Jet Interaction, Magnetically Arrested Flows, and Flares in Accreting Binary Black Holes
Abstract Supermassive binary black holes in galactic centers are potential multimessenger sources in gravitational waves and electromagnetic radiation. To find such objects, isolating unique electromagnetic signatures of their accretion flow is key. With the aid of three-dimensional general-relativistic magnetohydrodynamic simulations that utilize an approximate, semianalytic, superimposed spacetime metric, we identify two such signatures for merging binaries. Both involve magnetic reconnection and are analogous to plasma processes observed in the solar corona. The first, like colliding flux tubes that can cause solar flares, involves colliding jets that form an extended reconnection layer, dissipating magnetic energy and causing the two jets to merge. The second, akin to coronal mass ejection events, involves the accretion of magnetic field lines onto both black holes; these magnetic fields then twist, inflate, and form a trailing current sheet, ultimately reconnecting and driving a hot outflow. We provide estimates for the associated electromagnetic emission for both processes, showing that they likely accelerate electrons to high energies and are promising candidates for continuous, stochastic, and/or quasi-periodic higher-energy electromagnetic emission. We also show that the accretion flows around each black hole can display features associated with the magnetically arrested state. However, simulations with black hole spins misaligned with the orbital plane and simulations with larger Bondi radii saturate at lower values of horizon-penetrating magnetic flux than standard magnetically arrested disks, leading to weaker, intermittent jets owing to feedback from the weak jets or equatorial flux tubes ejected by reconnecting field lines near the horizon.
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- Award ID(s):
- 2307394
- PAR ID:
- 10567572
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 979
- Issue:
- 2
- ISSN:
- 2041-8205
- Format(s):
- Medium: X Size: Article No. L24
- Size(s):
- Article No. L24
- Sponsoring Org:
- National Science Foundation
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