具有核解离的球形吸积激波的稳定性
Stability of a Spherical Accretion Shock with Nuclear Dissociation
摘要：
我们研究的稳定性的驻激波内的球形吸积流到引力恒星，在核心坍缩超新星爆炸的背景下。我们的重点是冲击下方的核解离对冲击流体非径向振荡的线性增长和非线性饱和的影响。我们结合二维，时间相关的流体动力学模拟使用FLASH2.5与线性特征值问题的解决方案，并证明了这两种方法的一致性。以前对这种“静止吸积激波不稳定性”的研究要么侧重于无核离解的零能量吸积流，要么利用详细的有限温度核物质状态方程并包括强中微子加热。我们的主要目标是在这篇论文和随后的论文中引入状态方程的复杂性不断增加，以隔离各种竞争的影响。在这项工作中，我们采用了一个理想气体状态方程与一个恒定的核离解率低于冲击，不包括中微子加热。我们发现，一个负的伯努利参数低于冲击显着降低的实际频率，增长率和饱和振幅的SASI。绝热指数的减小具有类似的效果。不稳定性的非线性发展的特征是在几乎恒定的内能下，由湍流动能驱动的激波的膨胀。我们的研究结果还提供了进一步的洞察不稳定机制：一个特定的模式的增长速度是最快的径向平流时间从冲击的吸积物重叠的时期，一个常设的横向声波。因此，增长最快的模式可以通过核离解来改变。
英文摘要：
We examine the stability of a standing shock wave within a spherical accretion flow onto a gravitating star, in the context of core-collapse supernova explosions. Our focus is on the effect of nuclear dissociation below the shock on the linear growth, and non-linear saturation, of non-radial oscillations of the shocked fluid. We combine two-dimensional, time-dependent hydrodynamic simulations using FLASH2.5 with a solution to the linear eigenvalue problem, and demonstrate the consistency of the two approaches. Previous studies of this `Standing Accretion Shock Instability' (SASI) have focused either on zero-energy accretion flows without nuclear dissociation, or made use of a detailed finite-temperature nuclear equation of state and included strong neutrino heating. Our main goal in this and subsequent papers is to introduce equations of state of increasing complexity, in order to isolate the various competing effects. In this work we employ an ideal gas equation of state with a constant rate of nuclear dissociation below the shock, and do not include neutrino heating. We find that a negative Bernoulli parameter below the shock significantly lowers the real frequency, growth rate, and saturation amplitude of the SASI. A decrease in the adiabatic index has similar effects. The non-linear development of the instability is characterized by an expansion of the shock driven by turbulent kinetic energy at nearly constant internal energy. Our results also provide further insight into the instability mechanism: the rate of growth of a particular mode is fastest when the radial advection time from the shock to the accretor overlaps with the period of a standing lateral sound wave. The fastest-growing mode can therefore be modified by nuclear dissociation.
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