While the Advanced LIGO and Virgo gravitational-wave experiments now regularly observe binary black hole mergers, the evolutionary origin of these events remains a mystery. Analysis of the binary black hole spin distribution may shed light on this mystery, offering a means of discriminating between different binary formation channels. Using the data from Advanced LIGO and Virgo's first and second observing runs, here we seek to carefully characterize the distribution of effective spin among binary black holes, hierarchically measuring the distribution's mean $\mu$ and variance $\sigma^2$ while accounting for selection effects and degeneracies between spin and other black hole parameters. We demonstrate that the known population of binary black holes have spins that are both small, with $\mu \sim 0$, and very narrowly distributed, with $\sigma^2 \leq 0.07$ at 95% credibility. We then explore what these ensemble properties imply about the spins of individual binary black hole mergers, re-analyzing existing gravitational-wave events with a population-informed prior on their effective spin. The binary black hole GW170729, which previously excluded effective spin equal to zero, is now consistent with zero effective spin at ~10% credibility. More broadly, we find that uninformative spin priors generally yield overestimates for the effective spin magnitudes of compact binary mergers.

中文翻译：

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二元黑洞的低有效自旋及其对个别引力波事件的影响

虽然高级 LIGO 和室女座引力波实验现在定期观察双黑洞合并，但这些事件的进化起源仍然是个谜。对双黑洞自旋分布的分析可能会揭示这个谜团，提供一种区分不同双星形成通道的方法。使用来自 Advanced LIGO 和 Virgo 的第一次和第二次观测运行的数据，在这里我们试图仔细描述双黑洞之间有效自旋的分布，分层测量分布的均值 $\mu$ 和方差 $\sigma^2$，同时考虑自旋和其他黑洞参数之间的选择效应和退化。我们证明了已知的二元黑洞群具有很小的自旋，$\mu\sim 0$，并且分布非常窄，$\sigma^2 \leq 0.07$ 的可信度为 95%。然后，我们探索这些集合特性对单个双黑洞合并的自旋意味着什么，重新分析现有的引力波事件，并在有效自旋之前先了解群体。双黑洞 GW170729 之前排除了等于零的有效自旋，现在与零有效自旋一致，可信度约为 10%。更广泛地说，我们发现无信息自旋先验通常会高估紧凑二元并合的有效自旋幅度。之前排除了等于零的有效自旋，现在与零有效自旋一致，可信度约为 10%。更广泛地说，我们发现无信息自旋先验通常会高估紧凑二元并合的有效自旋幅度。之前排除了等于零的有效自旋，现在与零有效自旋一致，可信度约为 10%。更广泛地说，我们发现无信息自旋先验通常会高估紧凑二元并合的有效自旋幅度。