[论文解读] Eccentricity Estimate for Black Hole Mergers with Numerical Relativity Simulations

V. Gayathri, J. Healy+8 more|arXiv (Cornell University)|Sep 11, 2020

Pulsars and Gravitational Waves Research被引用 46

一句话总结

该论文进行611个离心和920个非离心的数值相对论模拟，以评估GW190521，发现其最为符合高离心并且通过贝叶斯因子量化的支持。

ABSTRACT

The origin of black hole mergers discovered by the LIGO and Virgo gravitational-wave observatories is currently unknown. GW190521 is the heaviest black hole merger detected so far. Its observed high mass and possible spin-induced orbital precession could arise from the binary having formed following a close encounter. An observational signature of close encounters is eccentric binary orbit; however, this feature is currently difficult to identify due to the lack of suitable gravitational waveforms. No eccentric merger has been previously found. Here we report 611 numerical relativity simulations covering the full eccentricity range and an estimation approach to probe the eccentricity of mergers. Our set of simulations corresponds to $\sim 10^5$ waveforms, comparable to the number used in gravitational wave searches, albeit with coarser mass-ratio and spin resolution. We applied our approach to GW190521 and found that it is the most consistent with a highly eccentric ($e=0.69^{+0.17}_{-0.22}$; 90% credible level) merger within our set of waveforms. This interpretation is supported over a non-eccentric merger with $>10$ Odds ratio if $\gtrsim10\%$ of GW190521-like mergers are highly eccentric. Detectable orbital eccentricity would be evidence against an isolated binary origin, which is otherwise difficult to rule out based on observed mass and spin.

研究动机与目标

• 说明离心度如何影响引力波形及合并起源。
• 开发一套覆盖不同离心率和自旋的大规模NR波形集合，以便对GR数据进行稳健比对。
• 利用贝叶斯参数估计和一致性检验，在离心NR波形框架下评估GW190521。
• 评估离心度对源属性和探测体积的影响。

提出的方法

• 使用RIFT框架直接将数值相对论波形与LIGO-Virgo数据进行比较。
• 在高斯似然下对外在参数（距离、天空位置、取向）以及红移后的质量进行边缘化。
• 按自旋和取向对波形进行分组，以分析离心度的依赖性。
• 使用波形一致性测试(cWB)来防止非高斯探测噪声的影响。
• 计算贝叶斯因子，比较高离心率与低离心率匹配。

实验结果

研究问题

• RQ1 GW190521是否能被高度离心的NR波形更好地描述，而不是非离心模型？
• RQ2 在离心NR波形框架下，重建的二元系统参数（质量、距离、离心度、自旋）是什么？
• RQ3 离心度推断对波形采样和先验选择的鲁棒性如何？
• RQ4 与非离心情景相比，离心度对可探测体积的影响如何？

主要发现

• 大约为76的贝叶斯因子偏向于GW190521的高离心（e>0.5）而非低离心。
• 在给定分析设置下，可以在90%置信度下排除零离心。
• 用离心NR波形拟合与非离心模型相比，重建的总质量和距离存在显著差异。
• 重建的离心模型的灵敏体积大致是非离心情形的两倍。
• 分析将GW190521信号识别为在NR波形集合中最符合高度离心合并的情形。
• 注入研究表明该方法能够区分高离心和零离心波形。