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arXiv 1409.4783astro-ph.SR
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核塌缩超新星的非径向不稳定性和前身星非球性

Non-Radial Instabilities and Progenitor Asphericities in Core-Collapse Supernovae

B. Müller, H. -Th. Janka

摘要:

由于核心坍缩超新星模拟仍然难以在3D中产生强大的中微子驱动的爆炸,因此有人提出,由祖先对流引起的非球面性可能会通过增强激波后区域非径向流体动力学不稳定性的活动来促进激波复兴。我们深入研究这种情况下,使用42个相对论二维模拟与多群中微子输运检查的速度和密度扰动的影响,在祖不同的扰动几何形状,遵守基本的物理约束(如滞弹性条件)。作为分析我们的结果的框架,我们引入半经验的标度律中微子加热,在增益区的平均湍流速度,和冲击变形的非径向不稳定性的饱和极限。湍流马赫数的平方<Ma^2>反映了增益层中非球面运动的剧烈程度,当<Ma^2>为~0.3时会发生爆炸性失控,这对应于临界中微子光度与一维相比降低了~25%。根据这一理论,先驱体的非球面性主要通过在激波上产生各向异性的质量流来帮助激波恢复:差分入流有效地将先驱体中的速度扰动转化为初始对流马赫数Ma量级的激波处的密度扰动(Delta rho/rho)。各向异性的质量通量和冲压压力使激波变形,从而放大激波后的湍流。大尺度(l=2,l=1)模态证明最有利于激波复苏,而小尺度扰动则需要不切实际的高对流马赫数。原始星系中的初始密度扰动只有Ma ^2量级,因此起着次优势作用。

英文摘要:

Since core-collapse supernova simulations still struggle to produce robust neutrino-driven explosions in 3D, it has been proposed that asphericities caused by convection in the progenitor might facilitate shock revival by boosting the activity of non-radial hydrodynamic instabilities in the post-shock region. We investigate this scenario in depth using 42 relativistic 2D simulations with multi-group neutrino transport to examine the effects of velocity and density perturbations in the progenitor for different perturbation geometries that obey fundamental physical constraints (like the anelastic condition). As a framework for analysing our results, we introduce semi-empirical scaling laws relating neutrino heating, average turbulent velocities in the gain region, and the shock deformation in the saturation limit of non-radial instabilities. The squared turbulent Mach number, <Ma^2>, reflects the violence of aspherical motions in the gain layer, and explosive runaway occurs for <Ma^2>~0.3, corresponding to a reduction of the critical neutrino luminosity by ~25% compared to 1D. In the light of this theory, progenitor asphericities aid shock revival mainly by creating anisotropic mass flux onto the shock: Differential infall efficiently converts velocity perturbations in the progenitor into density perturbations (Delta rho/rho) at the shock of the order of the initial convective Mach number Ma. The anisotropic mass flux and ram pressure deform the shock and thereby amplify post-shock turbulence. Large-scale (l=2,l=1) modes prove most conducive to shock revival, whereas small-scale perturbations require unrealistically high convective Mach numbers. Initial density perturbations in the progenitor are only of order Ma^2 and therefore play a subdominant role.

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