黑洞双星的三重诱导并合：恒星演化、动力学稳定性与自旋演化的作用综述
Triple-induced mergers of black hole binaries: A comprehensive look at the role of stellar evolution, dynamical stability, and spin evolution
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中文总结 AI 辅助
本研究通过种群合成与n体模拟，探究三星系统中黑洞双星的并合机制，得到稳定与不稳定三星系统的并合率密度，明确了并合黑洞的偏心率、有效自旋特征及相关动力学成因。
中文摘要 AI 辅助
黑洞（BH）并合已被证实是宇宙中普遍存在的现象，但我们对黑洞并合前演化的理论认识仍存在不确定性。黑洞前身星似乎主要形成于三星系统或更高阶的多星系统中，第三体的存在可对黑洞双星（BHB）产生足够的摄动，从而促发并合。我们结合种群合成与轨道平均的三重动力学描述，对一组初始轨道较宽、前身星质量较大的三星系统进行演化；选择宽轨道是为了避免黑洞形成前发生恒星相互作用。对于保持束缚并形成内黑洞双星的系统，我们采用包含2.5阶后牛顿项的直接n体代码进行演化，还通过将n体求解器与自旋的微分方程耦合，模拟了黑洞自旋矢量的进动。对于具有内黑洞双星的动力学稳定三星系统，其并合率密度估计约为~5 Gpc⁻³ yr⁻¹；在动力学不稳定的三星系统中也会发生并合，其率密度约为~1.4 Gpc⁻³ yr⁻¹。在进入10 Hz引力波频段时，正在并合的内双星呈现出10⁻⁴至10⁻²之间的偏心率。通过该通道并合的黑洞双星，其最终有效自旋可在-1至1之间呈现出很宽的取值范围，且略微倾向于χₑff≈0；这是由于在引力波辐射导致内双星收缩并与第三体解耦之前，正在并合的三星系统经历了强烈的三体动力学作用，内角动量可探索整个相空间，最终将有效自旋冻结在最高内偏心率时刻的取值。
英文摘要
Mergers of black holes (BHs) have been shown to be a ubiquitous phenomenon in the Universe. However, uncertainties remain in our theoretical understanding of the evolution of the BHs prior to their merger. Black hole progenitors are seemingly born primarily in triples or higher-order multiples, and the presence of a tertiary object can perturb a black hole binary (BHB) enough to precipitate a merger. We used population synthesis coupled with orbit-averaged descriptions of triple dynamics to evolve a population of triples with initially wide orbits and massive progenitors. Wide orbits were chosen to avoid stellar interaction prior to BH formation. Systems that remain bound and form an inner BHB were evolved using a direct n-body code with post-Newtonian terms up to an order of 2.5. We also simulated the precession of the BH spin vectors by coupling the n-body solver with the differential equations for the spins. For the dynamically stable triples with inner BHBs, mergers occur with an estimated rate density of $\sim 5$ Gpc$^{-3}$ yr$^{-1}$. Mergers also occur in triples that become dynamically unstable at a rate of $\sim 1.4$ Gpc$^{-3}$ yr$^{-1}$. At the point of entering the 10 Hz gravitational wave frequency band, the merging inner binaries exhibit eccentricities between $10^{-4}$ and $10^{-2}$. The final effective spin of a BHB that merges through this channel can display a wide range of values between $-1$ and $1$, with a slight tendency towards $χ_\text{eff} \approx 0$. This is a result of the strong three-body dynamics experienced by the merging triples before the inner binary begins to shrink due to GW emission. The inner angular momentum can explore the full phase space before the binary rapidly shrinks and decouples from the tertiary, effectively freezing out the effective spin to its value at the time of the highest inner eccentricity.
