Magnetically modified spherical accretion in GRMHD: reconnection-driven convection and jet propagation
Magnetically modified spherical accretion in GRMHD: reconnection-driven convection and jet propagation
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DOI：
10.1093/mnras/stab311
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发表时间：
2021-02
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影响因子：
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通讯作者：
S. Ressler;E. Quataert;C. White;O. Blaes
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作者：
S. Ressler;E. Quataert;C. White;O. Blaes
我们用三维广义相对论磁流体力学(GRMHD)模拟了一个快速旋转的黑洞周围的零角动量吸积，修正了初始均匀磁场的存在。我们考虑了磁场方向和黑洞自转之间的几个角度。在由此产生的流动中，中面动力学由磁重联驱动的湍流控制，处于磁阻滞(或近阻滞)状态。流出效率为∼10-200%的电磁急流占据极区，达到几百个引力半径，然后由于扭结不稳定性而消散。喷流方向随时间波动，相对于黑洞自转可以倾斜30∼◦，但这种倾斜并不强烈依赖于初始磁场的倾斜。即使在没有初始垂直净磁通量的情况下，也会形成喷流，因为湍流、水平尺度的波动可以在局部产生净垂直场。对于相对于黑洞自转倾斜40-80◦的初始磁场，可以获得峰值喷射功率，因为这最大化了可以到达黑洞的磁通量的量。对于SgrA*或M87这样的低光度黑洞吸积流，这些模拟可能是一个合理的模型。
We present 3D general relativistic magnetohydrodynamic(GRMHD) simulations of zero angular momentum accretion around a rapidly rotating black hole, modified by the presence of initially uniform magnetic fields. We consider serveral angles between the magnetic field direction and the black hole spin. In the resulting flows, the midplane dynamics are governed by magnetic reconnection-driven turbulence in a magnetically arrested (or a nearly arrested) state. Electromagnetic jets with outflow efficiencies ∼ 10–200% 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.