论文标题
扩展的宇宙中旋转黑洞的阴影
Shadow of a Spinning Black Hole in an Expanding Universe
论文作者
论文摘要
我们研究了宇宙扩张对共同观察者观察到的旋转黑洞阴影大小的影响。我们首先认为扩展仅由宇宙常数驱动，并在Kerr-DE保姆度量标准与FLRW度量标准之间建立联系。我们澄清说，一个共同观察者的概念在旋转黑洞的时空中只有在渐近的意义上。计算了共同观察者的阴影的角度大小。值得注意的是，对于遥远的观察者，角度大小接近非零有限值，而对于遥远的静态观察者而消失。此外，通过采用\ cite {bisnovatyi-kogan：2018vxl}中提出的近似方法，我们将研究扩展到一般的多组分宇宙案例。结果表明，水平和垂直角尺寸之间的差异发生了很大变化，而当超级质量旋转的黑洞处于高红移状态时，它们的比例（即填充性）保持不变，这是由于宇宙扩张所施加的常见扩增因子。此外，当$ a = 0 $时，我们的结果与\ cite {perlick：2018iye，bisnovatyi-kogan：2018vxl}的先前研究一致。
We study the influence of the cosmic expansion on the size of the shadow of a spinning black hole observed by a comoving observer. We first consider that the expansion is driven by a cosmological constant only and build the connection between the Kerr-de Sitter metric and the FLRW metric. We clarify that the notion of a comoving observer is well defined in the spacetime of a spinning black hole only in the sense of being asymptotic. The angular size of the shadow for a comoving observer is calculated. Significantly we find that the angular size approaches a non-zero finite value for a distant comoving observer, while it vanishes for a distant static observer. Furthermore, by adopting the approximate method proposed in \cite{Bisnovatyi-Kogan:2018vxl} we extend the study to the general multi-component universe case. The results show that the difference between the horizontal and vertical angular size changes a lot, while their ratio, i.e. the oblateness, keeps unchanged when the supermassive spinning black hole is at a high redshift, due to the common amplification factor exerted by the cosmic expansion. In addition, when $a=0$, our results agree with the previous studies in \cite{Perlick:2018iye,Bisnovatyi-Kogan:2018vxl}.
