AI 中文总结
本研究利用COSMIC代码探究双星演化不确定性对BNS形成效率与并合率的影响，识别出相关演化特征，发现模型参数间存在显著简并性，需第三代引力波观测突破约束。
AI 中文摘要
我们研究双星恒星演化的不确定性对双中子星（BNS）系统形成效率与宇宙学并合率的影响，尤其旨在确定能否在宽金属丰度范围内识别出双星演化的可靠特征。我们利用族群合成代码COSMIC，对72个双星演化模型开展系统探究，调整控制公共包层演化起始与效率、诞生kick（天体形成时的速度 kick）方案及公共包层阶段 kick 处理的四个关键参数；针对每个模型，采用多种宇宙金属丰度-红移关系方案计算BNS形成效率与宇宙学并合率。我们识别出BNS形成效率金属丰度依赖关系中的特征性结构，其源于特定演化过程，包括低金属丰度下首次巨星分支跳过的起始，以及Z=10⁻³到7.5×10⁻³之间的非单调演化。所有模型还预测BNS前身星质量呈双峰分布，对应两个不同形成通道。公共包层抛射效率与诞生kick方案仍是不确定性的主要来源，使BNS形成效率和宇宙学并合率产生数个数量级的变化。最后，我们表明不同双星演化参数组合可产生相似的并合率历史，凸显族群合成模型间存在显著简并性。当前引力波观测仅能排除效率最低的形成场景，要打破这些简并性，需未来第三代引力波天文台获取更多BNS并合样本，以及对宇宙时标上金属丰度演化的更优观测约束。
英文摘要
We investigate the impact of uncertainties in binary stellar evolution on the formation efficiency and cosmological merger rate of BNS systems. In particular, we aim to determine whether robust signatures of binary evolution can be identified across a broad range of metallicities. We perform a systematic exploration of 72 binary evolution models using the population synthesis code COSMIC. We vary four key parameters controlling the onset and efficiency of common-envelope evolution, the natal kick prescription, and the treatment of kicks during the common envelope phase. For each model, we compute the BNS formation efficiency and cosmological merger rate using several prescriptions for the cosmic metallicity-redshift relation. We identify characteristic features in the metallicity dependence of the BNS formation efficiency that arise from specific evolutionary processes. These include the onset of first-giant-branch skipping at low metallicity and a non-monotonic evolution between $Z=10^{-3}$ and $7.5\times 10^{-3}$. All models also predict a bimodal distribution of BNS progenitor masses associated with two distinct formation channels. The common envelope ejection efficiency and natal kick prescription remain the dominant sources of uncertainty, producing variations of several orders of magnitude in both the BNS formation efficiency and the cosmological merger rate. Finally, we show that different combinations of binary-evolution parameters can produce similar merger-rate histories, highlighting significant degeneracies among population-synthesis models. Current gravitational-wave observations can rule out only the least efficient formation scenarios. Breaking these degeneracies will require larger samples of BNS mergers expected from future third-generation gravitational-wave observatories, and improved observational constraints on the evolution of metallicity across cosmic time.
Comments18 pages, 9 figures
