Using Spin to Understand the Formation of LIGO and Virgo's Black Holes
Using Spin to Understand the Formation of LIGO and Virgo's Black Holes
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DOI：
10.3847/2041-8213/aaaa64
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发表时间：
2018-02-10
影响因子：
7.9
通讯作者：
Farr, Will M.
中科院分区：
文献类型：
--
作者：
Farr, Ben;Holz, Daniel E.;Farr, Will M.
随着高级LIGO和处女座探测器探测到越来越多的双黑洞（BBH）合并，人们有可能约束潜在群体的性质，并更好地了解这些系统的形成。黑洞（BH）的自旋方向是形成历史中最清晰的鉴别器之一，在密集恒星环境中动态形成的双星中，黑洞的自旋预计会各向同性分布，而在孤立的种群中，恒星演化预计会诱导自旋优先与轨道角动量对齐。在这项工作中，我们提出了一种简单的、与模型无关的方法来表征LIGO/Virgo的BBH群的自旋特性。通过测量双星的有效自旋，我们引入了一个简单的参数来量化各向同性分布的总体比例，而不管总体的自旋大小分布如何。一旦确定了星系群的方向特征，我们将展示如何使用有效自旋的测量来直接约束黑洞的自旋大小分布。我们发现，最有效的自旋测量值太小，无法提供信息，前四个事件显示出对对齐人群的轻微偏好，优势比为1.2。我们认为，通过数十个额外的检测，可以在高置信度下区分对称和反对称种群，尽管混合种群可能需要更长的时间来解开纠缠。我们还在排列或各向同性粒子群的假设下，从LIGO的前四个黑洞得到了黑洞自旋大小的分布。
With the growing number of binary black hole (BBH) mergers detected by the Advanced LIGO and Virgo detectors, it is becoming possible to constrain the properties of the underlying population and 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 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/Virgo's BBH population. Using measurements of the effective spin of the binaries, 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 BH spin magnitude distribution. We find that most effective spin measurements are too small to be informative, with the first four events showing a slight preference for a population with alignment, with an odds ratio of 1.2. 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 longer to disentangle. We also derive BH spin magnitude distributions from LIGO's first four BBHs under the assumption of aligned or isotropic populations.