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arXiv 2101.09008gr-qc
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Kerr和Kerr-Newman黑洞的强引力透镜

Strong gravitational lensing by Kerr and Kerr-Newman black holes

Tien Hsieh, Da-Shin Lee, Chi-Yong Lin

摘要:

研究了角动量为$a$的Kerr黑洞和附加电荷为$Q$的Kerr-Newman黑洞的强引力透镜.我们首先推导出当光线在光子球附近传播时特别发散的光线的偏转角的解析表达式。在这种强偏转极限下,光线在到达观察者之前可以绕黑洞多次,从而产生相对论图像。然后应用得到的解析表达式计算了超大质量星系黑洞的相对论像的角位置和放大率。在这项工作中,我们专注于参考光轴的最外图像。我们发现,它的角距离从一个最接近的光轴和放大倍数增加的角动量$a$的黑洞的光线与直接的轨道。此外,黑洞的电荷$Q$效应也增加了最外层像与其他像的角间距,以及直接和逆行轨道的放大率。我们将讨论角动量和黑洞电荷效应对相对论图像的潜在可观测性的增加。

英文摘要:

We study the strong gravitational lensing due to the Kerr black holes with angular momentum $a$ and the Kerr-Newman black holes with additional charge $Q$. We first derive the analytical expressions of the deflection angles of light rays that particularly diverge as they travel near the photon sphere. In this strong deflection limit, the light rays can circle around the black hole multiple times before reaching the observer, giving relativistic images. The obtained analytical expressions are then applied to compute the angular positions and the magnifications of relativistic images due to the supermassive galactic black holes. In this work, we focus on the outermost image with reference to the optical axis. We find that its angular separation from the one closest to the optical axis and the magnification increase in angular momentum $a$ of the black holes for light rays with direct orbits. Additionally, the effects of the charge $Q$ of black holes also increase the angular separation of the outermost image from the others and the magnification for both direct and retrograde orbits. The potentially increasing observability of the relativistic images from the effects of angular momentum and charge of the black holes will be discussed.

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