通过总自旋测量双黑洞并合中的自旋-轨道错位
Measurement of spin-orbit misalignment in binary black holes via the total spin
- Northwestern University（西北大学）
- University of California at Santa Barbara（加州大学圣塔芭芭拉分校）
- California Institute of Technology（加州理工学院）
- The University of Chicago（芝加哥大学）
- Institute for Advanced Study（高等研究院）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本研究引入θ_LS作为自旋-轨道错位的替代测量指标，通过合成观测和GWTC-5.0星表分析，发现双黑洞种群需显著自旋-轨道错位，且识别出此前未发现的自旋不对齐事件。
AI中文摘要：
并合双黑洞中的自旋-轨道对齐程度是探测其形成历史的有力工具。然而，评估单个事件中的自旋-轨道错位仍具挑战性，因为大多数用于表征进动的常用参数往往约束不足。本研究引入总自旋与轨道角动量之间的夹角θ_LS作为自旋-轨道错位的替代测量指标。利用合成观测数据，我们表明θ_LS在区分自旋对齐与各向同性自旋假设时，保留的信息多于包括χ_p在内的常用替代指标。随后，我们对GWTC-5.0星表中观测到的双黑洞并合事件研究该参数，发现多个与自旋对齐不符的事件。在若干案例中，仅从有效自旋参数（χ_p或χ_eff）或单个自旋-轨道倾角（θ₁或θ₂）的后验分布中无法看出这一点，因此此前未被识别。我们特别指出GW241127_061008作为第二代并合的典型案例，其具有大且倾斜的初级自旋、不等质量，且初级质量接近对不稳定超新星质量间隙。最后，我们利用cosθ_LS进行种群推断，确认双黑洞种群既不符合纯各向同性分布，也不符合纯自旋对齐分布，而需要显著的自旋-轨道错位。
英文摘要：
The degree of spin-orbit alignment in merging binary black holes is a powerful probe of their formation history. However, assessing spin-orbit misalignment in individual events remains challenging, as most parameters commonly used to characterize precession tend to be poorly constrained. In this work, we introduce the angle between the total spin and orbital angular momentum, $θ_{LS}$, as an alternative measure of spin-orbit misalignment. Using synthetic observations, we show that $θ_{LS}$ retains more information to discriminate between the aligned- and isotropic-spins hypotheses than commonly used alternatives, including $χ_{\rm p}$. We then study this parameter on binary black hole mergers observed in the GWTC-5.0 catalog, and identify multiple events that are inconsistent with having aligned spins. In several of the examples, this is not apparent from the posteriors of the effective spin parameters ($χ_{\rm p}$ or $χ_\mathrm{eff}$) nor the individual spin-orbit tilts ($θ_1$ or $θ_2$) alone, and thus had not been previously identified. We highlight GW241127_061008 as a compelling case for a second-generation merger, with a large, tilted primary spin, unequal masses, and a large primary mass near the pair-instability-supernova mass gap. Finally, we perform population inference using $\cosθ_{LS}$ and confirm that the binary black hole population is inconsistent with either a purely isotropic or a purely aligned-spin distribution, and requires substantial spin-orbit misalignment.
