Numerical Simulations of Relativistic Jet Formation in Kerr Black Hole Magnetosphere

人们已经发现了来自宇宙中几种物体的相对论喷流。人们认为它们都是由黑洞附近的暴力现象形成的。在已提出的机制中，形成喷流的磁性机制是最有希望的，因为它不仅可以解释喷流的加速，而且可以解释喷流的准直。然而，不同的机制尚未显示出来。为了研究磁机制，我们开发了广义相对论磁流体动力学(GRMHD)模拟程序。第一年，我们对由克尔黑洞、稀有均匀等离子体和强均匀磁场组成的相当简单的系统进行了GRMHD模拟。结果很好地显示了黑洞在磁场中产生的强功率辐射。有趣的是，它还展示了黑洞能量提取的磁性机制。然而，大多数等离子体落入黑洞，没有形成喷流。然后，我们对径向磁场和电流环在黑洞附近感应磁场的情况进行了GRMHD模拟。通过这些计算，我们成功地显示了相对论流出，其速度大于光速的90%。特别是，在电流环磁场的情况下，连接在黑洞周围的磁层和吸积盘之间的磁通管被快速的框架拖拽扭曲。磁管(磁桥)中磁压的增加导致磁桥的爆炸性膨胀。数值结果表明，膨胀产生了相对论外流。总之，克尔黑洞周围的磁力层和吸积盘之间的磁桥从来都不是稳态的，应该与相对论喷流直接相连。

Relativistic jets from several kinds of objects in the universe have been found. It is believed that they are all formed by violent phenomena near the black holes. Among the proposed mechanisms, the magnetic mechanism of the jet formation is becaming most promising because it may explain not only the acceleration but also the collimation of the jets. However, the distinct mechanism has not yet been shown. To investigate the magnetic mechanism, we have developed the general relativistic magnetchydrodynamic (GRMHD) simulation code.First year of this research project, we have performed the GRMHD simulation of the rather simple system consisting of the Kerr black hole, rare uniform plasma, and the strong uniform magnetic field. The result dearly showed the strong power radiation from the black hole through the magnetic field. It also interestingly showed the magnetic mechanism of the energy extraction of the black hole. However, most of the plasma falls into the black hole and no jet is formed. Then, next we performed the GRMHD simulation of the cases with the radial magnetic field and the magnetic field induced by the electric current loop near the black hole. With these calculations, we have succeeded to show the relativistic outflow, whose velocity is larger than 90% of light speed. Especially, in the current loop magnetic field case, the magnetic flux tubes bridging the region between the ergosphere and the accretion disk around the black hole are twisted by the frame-dragging rapidly. The increase in the magnetic pressure in the magnetic tubes (magnetic bridge) causes the explosive expansion of the magnetic bridges. The numerical results show that the expansion produces the relativistic outflow. In conclusion, the magnetic bridge between the ergosphere and the accretion disk around the Kerr black hole never be steady-state and should be connected to the relativistic jets directly.