大尺度磁场作用下气体介质中的动力学摩擦
Dynamical friction in a gaseous medium with a large-scale magnetic field
摘要：
一个大质量引力体在气体介质中运动时所受到的动力学摩擦力会被足够强的大尺度磁场所改变。利用线性微扰理论，我们计算了在均匀磁化介质中沿直线运动的物体产生的尾流结构和重力拖曳力。阻力作为马赫数的函数的函数形式（V_0/c_s，其中V_0是物体的速度，c_s是声速）取决于磁场的强度和扰动速度与磁场方向之间的夹角。特别地，对于在充分磁化的介质中运动的扰动体，拖曳力的峰值不在马赫数1附近。根据经验，我们可以说，对于超音速运动，磁场起到抑制动力学摩擦的作用;对于亚音速运动，磁场倾向于增强动力学摩擦。对于沿磁场线运动的扰动，在某些亚音速马赫数下的阻力可能比超音速时的阻力更大。我们还提到了我们的研究结果的相关性，黑洞合并在星系核。
英文摘要：
The dynamical friction force experienced by a massive gravitating body moving through a gaseous medium is modified by sufficiently strong large-scale magnetic fields. Using linear perturbation theory, we calculate the structure of the wake generated by, and the gravitational drag force on, a body traveling in a straight-line trajectory in a uniformly magnetized medium. The functional form of the drag force as a function of the Mach number (V_0/c_s, where V_0 is the velocity of the body and c_s the sound speed) depends on the strength of the magnetic field and on the angle between the velocity of the perturber and the direction of the magnetic field. In particular, the peak value of the drag force is not near Mach number 1 for a perturber moving in a sufficiently magnetized medium. As a rule of thumb, we may state that for supersonic motion, magnetic fields act to suppress dynamical friction; for subsonic motion, magnetic fields tend to enhance dynamical friction. For perturbers moving along the magnetic field lines, the drag force at some subsonic Mach numbers may be stronger than it is at supersonic velocities. We also mention the relevance of our findings to black hole coalescence in galactic nuclei.
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