中子星自旋的SASI螺旋模引起的Angular momentum再分布和结果
Angular momentum redistribution by SASI spiral modes and consequences for neutron star spins
摘要：
在大质量恒星坍缩的核心中，稳定的吸积激波不稳定性（SASI）可以驱动螺旋模式，有效地重新分配角动量。这个过程可以赋予形成中的中子星自旋，即使其前身星是不旋转的。在这里，我们开发的第一个分析描述的角动量重新分配驱动的螺旋模式的SASI。我们的分析，有效的小模式振幅的限制，表明角动量分离驱动的雷诺应力产生的螺旋模式。所得的解决方案相比，毫不逊色与以前的三维流体动力学模拟的SASI在线性和弱非线性阶段。合理的协议时，也发现外推到完全非线性阶段的解决方案。在这些模拟的饱和状态下进行了流的Hellows分解，表明由雷诺应力和质量通量的波动分量平衡的向外角动量输送由平流向内输送。推导出了沉积在中子星中的最大角动量与质量吸积率、冲击波半径、冲击波压缩比和爆炸时螺旋模式振幅的函数关系的近似解析表达式。讨论了中子星的诞生自旋周期的意义。
英文摘要：
In the collapsing core of massive stars, the standing accretion shock instability (SASI) can drive spiral modes that efficiently redistribute angular momentum. This process can impart a spin to the forming neutron star even when the progenitor star is non-rotating. Here we develop the first analytical description of the angular momentum redistribution driven by a spiral mode of the SASI. Our analysis, valid in the limit of small mode amplitude, shows that the angular momentum separation is driven by the Reynolds stress generated by the spiral mode. The resulting solutions compare favorably with previous three-dimensional hydrodynamic simulations of the SASI in the linear and weakly non-linear phases. Reasonable agreement is also found when extrapolating the solutions into the fully non-linear phase. A Reynolds-decomposition of the flow is performed in the saturated state of these simulations, showing that outward angular momentum transport by the Reynolds stress and the fluctuating component of the mass flux balance inward transport by advection. We derive an approximate analytic expression for the maximum angular momentum deposited in the neutron star as a function of the mass accretion rate, shock radius, shock compression ratio, and amplitude of the spiral mode at the time of explosion. Implications for the birth spin periods of neutron stars are discussed.
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