高超音速铅弹：作为非均匀准直等离子体团的天体物理喷流
Hypersonic Buckshot: Astrophysical Jets as Heterogeneous Collimated Plasmoids
摘要：
赫比格-哈罗（HH）射流通常被认为是以高超音速运动的均匀等离子体束。射流束内的结构通常归因于射流源处的条件的周期性或"脉冲“变化。基于这种情况的模拟导致结延伸穿过射流直径。观测和最近的高能量密度实验室实验揭示了低于这个尺度的结构，并表明它们可能对理解射流动力学的基本原理很重要。在本文中，我们提供了一个替代的“脉冲”模型的原恒星喷流。使用直接的数值模拟，我们探讨的可能性，射流是通过移动的块间介质传播的子径向块链。我们的模型探索了一个理想化的这种情况下，注入小（$r<r_{jet}$），密集（$ρ>ρ_{jet}$）的球体嵌入在一个否则光滑的簇间射流。球体以与射流速度相差$\sim15$ %的速度初始化。我们发现，从同质流到异质流的转变的后果是显着的团块相互作用，并以各种方式与团块间介质。可以形成模拟脉冲射流模型预期的结构，也可以形成以前看不见的“亚径向”行为，包括向后的弓形激波和离轴工作表面。虽然这些小规模的结构以前没有在模拟研究中看到过，但它们在高分辨率喷流观测中被发现。我们讨论了我们的模拟解释的原恒星喷气机方面的表征结的“寿命”或“速度历史”的方法，以及连接观察到的结构与中央引擎产生的喷气机的影响。
英文摘要：
Herbig-Haro (HH) jets are commonly thought of as homogeneous beams of plasma traveling at hypersonic velocities. Structure within jet beams is often attributed to periodic or ``pulsed'' variations of conditions at the jet source. Simulations based on this scenario result in knots extending across the jet diameter. Observations and recent high energy density laboratory experiments shed new light on structures below this scale and indicate they may be important for understanding the fundamentals of jet dynamics. In this paper we offer an alternative to ``pulsed'' models of protostellar jets. Using direct numerical simulations we explore the possibility that jets are chains of sub-radial clumps propagating through a moving inter-clump medium. Our models explore an idealization of this scenario by injecting small ($r<r_{jet}$), dense ($ρ>ρ_{jet}$) spheres embedded in an otherwise smooth inter-clump jet flow. The spheres are initialized with velocities differing from the jet velocity by $\sim15$%. We find the consequences of shifting from homogeneous to heterogeneous flows are significant as clumps interact with each other and with the inter-clump medium in a variety of ways. Structures which mimic what is expected from pulsed-jet models can form, as can previously unseen ``sub-radial'' behaviors including backward facing bow shocks and off-axis working surfaces. While these small-scale structures have not been seen before in simulation studies, they are found in high resolution jet observations. We discuss implications of our simulations for the interpretation of protostellar jets with regard to characterization of knots by a ``lifetime'' or ``velocity history'' approach as well as linking observed structures with central engines which produce the jets.
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