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arXiv 1709.07896astro-ph.HEgr-qc
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利用自旋理解LIGO的黑洞的形成

Using spin to understand the formation of LIGO's black holes

Ben Farr, Daniel E. Holz, Will M. Farr

摘要:

随着迄今为止先进LIGO探测器对四个候选双星黑洞(BBH)合并的探测,为了更好地理解这些系统的形成,限制BBH合并种群的属性变得可能。黑洞(BH)的自旋方向是形成历史的最干净的鉴别器之一,在稠密的恒星环境中动态形成的双星中的BH预计具有各向同性分布的自旋,与孤立的人口相反,恒星演化预计会诱导BH自旋优先与轨道角动量对齐。在这项工作中,我们提出了一个简单的,模型不可知的方法来表征自旋性质的LIGO的BBH人口。使用测量的有效自旋的二进制文件,这是LIGO的最佳约束自旋参数,我们引入了一个简单的参数来量化的人口是各向同性分布的分数,无论人口的自旋幅度分布。一旦人口的取向特性已经确定,我们展示了如何测量有效自旋可以用来直接约束底层BH自旋幅度分布。虽然我们发现目前大多数有效的自旋测量值都太小而无法提供信息,但对于LIGO的四个BBH候选者,我们发现具有对齐自旋的底层人口略优于具有各向同性自旋的人口(优势比为1.1)。我们认为,这将是有可能区分对称和反对称人口在高置信度与数十个额外的检测,虽然混合人口可能需要更多的检测解开。我们还推导出初步的自旋大小分布LIGO的黑洞,假设对齐或各向同性的人口。

英文摘要:

With the detection of four candidate binary black hole (BBH) mergers by the Advanced LIGO detectors thus far, it is becoming possible to constrain the properties of the BBH merger population in order to better understand the formation of these systems. Black hole (BH) spin orientations are one of the cleanest discriminators of formation history, with BHs in dynamically formed binaries in dense stellar environments expected to have spins distributed isotropically, in contrast to isolated populations where stellar evolution is expected to induce BH spins preferentially aligned with the orbital angular momentum. In this work we propose a simple, model-agnostic approach to characterizing the spin properties of LIGO's BBH population. Using measurements of the effective spin of the binaries, which is LIGO's best constrained spin parameter, we introduce a simple parameter to quantify the fraction of the population that is isotropically distributed, regardless of the spin magnitude distribution of the population. Once the orientation characteristics of the population have been determined, we show how measurements of effective spin can be used to directly constrain the underlying BH spin magnitude distribution. Although we find that the majority of the current effective spin measurements are too small to be informative, with LIGO's four BBH candidates we find a slight preference for an underlying population with aligned spins over one with isotropic spins (with an odds ratio of 1.1). We argue that it will be possible to distinguish symmetric and anti-symmetric populations at high confidence with tens of additional detections, although mixed populations may take significantly more detections to disentangle. We also derive preliminary spin magnitude distributions for LIGO's black holes, under the assumption of aligned or isotropic populations.

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