两种磁流体动力学鞘射流
Two Types of Magnetohydrodynamic Sheath Jets
摘要：
最近对来自不同星系核的天体物理喷流的观测强烈表明，双层结构或脊鞘结构可能是它们的共同特征。我们建议，这样的鞘射流结构可以形成磁流体动力学内的磁压力，这是由于极向和环向分量的峰值之间形成的谷，与作用在旋转鞘等离子体的离心力是平衡的环向场的环向应力。集中在极轴附近的极向场由朝向射流区域的会聚等离子体流维持，并且由于极向电流循环通过射流而在射流锥外形成环向场。在这种情况下，磁流体动力学（MHD）方程组允许两种主要类型的解决方案，至少，在该区域远离脚点。第一类解描述的是边界约束射流。当射流温度像病毒一样下降时，这种类型就实现了，并且压力梯度和MHD力都是一致确定的，即使在无穷远处也不能完全克服重力。第二类是在等温条件下实现的，重力完全被压力梯度力抵消。因此，这种类型的射流完全由MHD力加速。这也表明，这两种类型的对应，分别从第一和第二类射电星系的Fanaroff-Riley分类的喷流。
英文摘要：
Recent observations of astrophysical jets emanating from various galactic nuclei strongly suggest that a double layered structure, or a spine-sheath structure, is likely to be their common feature. We propose that such a sheath jet structure can be formed magnetohydrodynamically within a valley of the magnetic pressures, which is formed between the peaks due to the poloidal and toroidal components, with the centrifugal force acting on the rotating sheath plasma is balanced by the hoop stress of the toroidal field. The poloidal field concentrated near the polar axis is maintained by a converging plasma flow toward the jet region, and the toroidal field is developed outside the jet cone owing to the poloidal current circulating through the jet. Under such situations, the set of magnetohydrodynamic (MHD) equations allows two main types of solutions, at least, in the region far from the footpoint. The first type solution describes the jets of marginally bound nature. This type is realized when the jet temperature decreases like viral one, and neither the pressure-gradient nor the MHD forces, which are both determined consistently, cannot completely overcome the gravity even at infinity. The second type is realized under an isothermal situation, and the gravity is cancelled exactly by the pressure-gradient force. Hence, the jets of this type are accelerated purely by the MHD force. It is suggested also that these two types correspond, respectively, to the jets from type I and II radio galaxies in the Fanaroff-Riley classification.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
