Magnetic reconnection and plasmoid formation in three-dimensional accretion flows around black holes
Magnetic reconnection and plasmoid formation in three-dimensional accretion flows around black holes
复制标题
黑洞周围三维吸积流中的磁重联和等离子体团形成
DOI：
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发表时间：
2021
期刊：
影响因子：
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通讯作者：
L. Rezzolla
中科院分区：
文献类型：
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作者：
A. Nathanail;Vasilis Mpisketzis;O. Porth;C. Fromm;L. Rezzolla
磁重联被认为是向黑洞附近的等离子体提供能量的主要能量耗散机制之一。事实上，通过磁重联形成的等离子体团可能在银河系中心黑洞 SgrA* 的 γ 射线、X 射线和近红外耀斑中发挥关键作用。我们报告了三维广义相对论理想和电阻磁流体动力学模拟的结果，模拟了天体物理黑洞周围吸积流中的磁重联。与类似工作的一个重要区别是，我们的吸积盘具有初始偶极磁场配置，其中包含交替极性的环。我们表明，当前的片层是在黑洞吸积的湍流环境中快速形成和破坏的。等离子体团是由靠近事件视界的当前片层形成的，区域内的引力半径约为 2 − 15。我们进一步量化磁耗散和能量转移到等离子体团的过程，报告重连接率、相对于局部磁场的相对电流密度以及等离子体团的大小。我们发现等离子体团通过重新连接获得能量并加热到相对论温度，其中最大的等离子体团具有足够的能量以离开极地附近的黑洞。在它们的演化过程中，等离子体团被拉伸和拉长，当剪切力足够大时就会被破坏，尽管一些等离子体团在距黑洞约 30 − 40 引力半径的距离处以良好的结构形式存在。最后，我们发现，在某些情况下，等离子体团获得了超开普勒方位角速度，正如最近对 Sgr A* 耀斑的观测所表明的那样。
Magnetic reconnection is thought to be one of the main energy-dissipation mechanisms fu-eling energy to the plasma in the vicinity of a black hole. Indeed, plasmoids formed through magnetic reconnection may play a key role in γ -ray, X-ray and near-infrared flares from the black hole at the center of our galaxy, SgrA*. We report the results of three-dimensional general-relativistic ideal and resistive magnetohydrodynamics simulations modelling magnetic reconnection in accretion flows around astrophysical black holes. As an important dif-ference with similar works, our accretion discs have an initial dipolar magnetic-field configuration with loops of alternating polarity. We show that current sheets are formed and destroyed rapidly in the turbulent environment of black-hole accretion. Plasmoids are formed from current sheets close to the event horizon, in a region of ∼ 2 − 15 gravitational radii. We further quantify the magnetic dissipation and the process of energy transfer to the plasmoids, reporting the reconnection rate, the relative current density with respect to the local magnetic field, and the size of the plasmoids. We find that plasmoids gain energy through reconnection and heat up to relativistic temperatures, with the largest ones being sufficiently energetic to leave the black hole near the polar regions. During their evolution, plasmoids are stretched and elongated, becoming disrupted when the shear is sufficiently large, although some plasmoids survive as well-distinguished structures at distances of ∼ 30 − 40 gravitational radii from the black hole. Finally, we find that in some cases the plasmoids acquire a super-Keplerian azimuthal velocity, as suggested by recent observations of flares from Sgr A*.