We study the small scale magnetic reconnection above the radiative inefficient accretion flow around massive black hole via 2D magnetohydrodynamics (MHD) numerical simulation, in order to model the blob formation and ejection from the accretion flow around Sgr A*. The connection of both the newly emerging magnetic field and the pre-existing magnetic field is investigated to check whether blobs could be driven in the environment of black hole accretion disc. After the magnetic connection, both the velocity and temperature of the plasma can be comparable to the inferred physical properties at the base of the observed blob ejection. For illustration, three small boxes which are located within 40 Schwarzschild radii from the central black hole are chosen as our simulation areas. At the beginning of the reconnections, the fluid is pulled toward the central black hole due to the gravitational attraction and the current sheet produced by the reconnection is also pulled toward the same direction, consequently, the resulting outflows move both upwards and towards the symmetry axis of the central black hole. Eventually, huge blobs appear, which supports the catastrophe model of episodic jets \citep{2009MNRAS.395.2183Y}. It is also found that the closer to the black hole the magnetic connection happens, the higher the converting efficiency of the magnetic energy into the heat and kinetic energy. For these inner blobs, they have vortex structure due to the K-H instability, which happens along the current sheet separating the fluids with different speed.

中文翻译：

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大质量黑洞周围低效率的辐射吸积流的斑点形成和喷射

我们通过二维磁流体动力学 (MHD) 数值模拟研究了大质量黑洞周围辐射低效吸积流上方的小尺度磁重联，以模拟人马座 A* 周围吸积流的斑点形成和喷射。研究新出现的磁场和预先存在的磁场的联系，以检查在黑洞吸积盘的环境中是否可以驱动斑点。磁连接后，等离子体的速度和温度都可以与观察到的斑点喷射的基础上推断出的物理特性相媲美。为说明起见，我们选择了位于距离中心黑洞 40 Schwarzschild 半径内的三个小盒子作为我们的模拟区域。在重新连接的开始，由于万有引力，流体被拉向中心黑洞，重联产生的电流片也被拉向同一方向，因此，由此产生的流出物既向上又向中心黑洞的对称轴移动。最终，出现了巨大的斑点，这支持了偶发喷射\citep{2009MNRAS.395.2183Y}的灾难模型。还发现磁连接越靠近黑洞，磁能转化为热能和动能的效率就越高。对于这些内部斑点，由于 KH 不稳定性，它们具有涡流结构，这种不稳定性沿着以不同速度分离流体的电流片发生。