[论文解读] Do electron-capture supernovae make neutron stars? First multidimensional hydrodynamic simulations of the oxygen deflagration

Samuel Jones, F. K. Roepke+4 more|arXiv (Cornell University)|Feb 18, 2016

Gamma-ray bursts and supernovae参考文献 72被引用 56

一句话总结

本研究首次对氧-氖核心中的氧爆燃进行了多维流体动力学模拟，采用水平集火焰模型，探究电子捕获超新星和吸积诱导塌缩是否会产生中子星。结果表明，在中等和低点火密度下，核心会以接近一倍太阳质量的物质被抛射而爆炸，留下质量低于钱德拉塞卡极限的稳定残骸；仅在最高点火密度（log₁₀ρ_c = 10.3）时，才会发生塌缩形成中子星。

ABSTRACT

In the classical picture, electron-capture supernovae and the accretion-induced collapse of oxygen-neon white dwarfs (ONeWDs) undergo an oxygen deflagration phase before gravitational collapse produces a neutron star (NS). These types of core collapse events are postulated to explain several astronomical phenomena. In this work, the deflagration phase is simulated for the first time using multidimensional hydrodynamics, with the aim of gaining new insight into the explosive deaths of $8-10~M_\odot$ stars and ONeWDs that accrete material from a binary companion star. The main aim is to determine whether these events are thermonuclear or core-collapse supernova explosions, and hence whether NSs are formed by such phenomena. The deflagration is simulated in ONe cores with three different central ignition densities. The intermediate density case is perhaps the most realistic, being based on recent nuclear physics calculations and 1D stellar models. The 3D hydrodynamic simulations presented in this work begin from a centrally confined flame structure using a level-set-based flame approach and are performed in $256^3$ and $512^3$ numerical resolutions. In the simulations with intermediate and low ignition density, the cores do not appear to collapse into NSs. Instead, almost a solar mass of material becomes unbound from the cores, leaving bound remnants. These simulations represent the case in which semiconvective mixing during the electron-capture phase preceding the deflagration is inefficient. The masses of the bound remnants double when Coulomb corrections are included in the EoS, however they still do not exceed the effective Chandrasekhar mass and, hence, would not collapse into NSs. The simulations with the highest ignition density ($\log_{10}ρ_{ m c}=10.3$), representing the case where semiconvective mixing is very efficient, show clear signs that the core will collapse into a NS.

研究动机与目标

• 确定电子捕获超新星和氧-氖白矮星的吸积诱导塌缩是否会产生中子星。
• 研究多维流体动力学与湍流火焰传播在氧爆燃驱动爆炸中的作用。
• 评估中心点火密度、半对流混合效率以及方程状态修正对核心残骸质量的影响。
• 评估爆燃阶段是否导致核心塌缩或爆炸性解体。

提出的方法

• 模拟采用基于水平集的火焰方法，模拟3D流体动力学中的湍流爆燃，避免直接解析火焰前缘。
• 采用三种中心点火密度：低（log₁₀ρ_c = 10.0）、中等（log₁₀ρ_c = 10.15）和高（log₁₀ρ_c = 10.3），其中中等情形基于1D恒星模型和核物理数据。
• 在256³和512³网格点上测试数值分辨率，以评估收敛性和数值鲁棒性。
• 状态方程包含库仑修正，以评估其对残骸质量和稳定性的影响。
• 引入扰动以激发流体不稳定性，特别是瑞利-泰勒不稳定性，以检验对不对称性的敏感性。
• 模拟追踪电子分数（Yₑ）和能量释放，以评估核燃烧进程和爆炸能量学。

实验结果

研究问题

• RQ1 简并态氧-氖核心中的氧爆燃是否导致核心塌缩并形成中子星，还是仅引发热核爆炸？
• RQ2 中心点火密度如何影响结果——是爆炸性解体还是引力塌缩？
• RQ3 半对流混合效率和方程状态修正在多大程度上影响最终残骸质量？
• RQ4 多维流体动力学能否再现1D模型中观察到的火焰不对称性和湍流燃烧？
• RQ5 初始火焰几何形状和扰动在决定爆炸动力学和核合成中起什么作用？

主要发现

• 在中等和低点火密度下（log₁₀ρ_c = 10.15 和 10.0），核心经历爆炸性燃烧，抛射近似一倍太阳质量的物质，留下低于钱德拉塞卡质量的束缚残骸。
• 即使包含库仑修正，中等和低密度情形下的束缚残骸质量也未超过有效钱德拉塞卡质量，因此无法形成中子星。
• 仅在最高点火密度（log₁₀ρ_c = 10.3）时，对应于高效的半对流混合，核心显示出明显的引力塌缩迹象，最终形成中子星。
• 瑞利-泰勒不稳定性显著驱动火焰前缘的非球对称性，即使在层流状态下亦然，表明3D流体动力学对精确建模至关重要。
• 在中等密度情形下，湍流燃烧速度仅在约460 ms后才超过层流速度，表明湍流虽增强燃烧，但不会引发塌缩。
• 模拟表明，1D模型不足以预测全局结果，因其无法解析不对称性和流体不稳定性。