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arXiv 2107.11902astro-ph.HEgr-qc
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从双黑洞引力波观测推断形成时的自旋倾斜角:连接进动平均与轨道平均自旋演化

Inferring spin tilts at formation from gravitational wave observations of binary black holes: Interfacing precession-averaged and orbit-averaged spin evolution

Nathan K. Johnson-McDaniel, Sumeet Kulkarni, Anuradha Gupta

AI总结:

本文提出一种结合进动平均与轨道平均演化的新代码,从引力波观测推断双黑洞形成时的自旋倾斜角,并应用于 GW190521 等 O3a 事件,同时正则化方程以处理近等质量极限。

摘要:

从进动黑洞双星引力波信号中推断出的两个重要参数是自旋倾斜角,即黑洞自旋轴相对于双星轨道角动量的倾斜角度。LIGO-Virgo 参数估计分析目前给出的是在基准参考频率处的自旋倾斜角,通常是数据分析中使用的最低频率。然而,天体物理学上最感兴趣的量是双星形成时的自旋倾斜角,对于强进动双星,形成时的倾斜角可能与参考频率处的倾斜角存在显著差异。在形式上的无穷远距离处的自旋倾斜角是许多形成渠道中形成时倾斜角的良好近似,并且可以利用进动平均演化对双黑洞进行高效计算。在此,我们提出了一个新的代码,用于计算无穷远处的倾斜角,该代码将进动平均演化与高频处的轨道平均演化相结合,并展示了其在 GW190521 以及 O3a 中其他双黑洞探测事件中的应用。我们通过经验确定了轨道平均演化与进动平均演化之间的过渡频率,以在给定精度下产生无穷远处的倾斜角。我们还对进动平均方程进行了正则化处理,以便在实际中遇到的非常接近等质量的双星参数下获得良好的精度。这还使我们能够研究进动平均表达式的奇异等质量极限,在该极限下,我们发现其随质量比 q 存在近似为 1/(1 - q) 的标度关系。

英文摘要:

Two important parameters inferred from the gravitational wave signals of binaries of precessing black holes are the spin tilt angles, i.e., the angles at which the black holes' spin axes are inclined with respect to the binary's orbital angular momentum. The LIGO-Virgo parameter estimation analyses currently provide spin tilts at a fiducial reference frequency, often the lowest frequency used in the data analysis. However, the most astrophysically interesting quantities are the spin tilts when the binary was formed, which can be significantly different from those at the reference frequency for strongly precessing binaries. The spin tilts at formally infinite separation are a good approximation to the tilts at formation in many formation channels and can be computed efficiently for binary black holes using precession-averaged evolution. Here, we present a new code for computing the tilts at infinity that combines the precession-averaged evolution with orbit-averaged evolution at high frequencies and illustrate its application to GW190521 and other binary black hole detections from O3a. We have empirically determined the transition frequency between the orbit-averaged and precession-averaged evolution to produce tilts at infinity with a given accuracy. We also have regularized the precession-averaged equations in order to obtain good accuracy for the very close-to-equal-mass binary parameters encountered in practice. This additionally allows us to investigate the singular equal-mass limit of the precession-averaged expressions, where we find an approximate scaling of $1/(1 - q)$ with the mass ratio $q$.

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