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arXiv 2104.07889gr-qc
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Kerr黑洞附近零- angular-momentum源的可观测性

Observability of Zero-angular-momentum Sources Near Kerr Black Holes

Haopeng Yan, Minyong Guo, Bin Chen

摘要:

我们重新审视了克尔黑洞附近零角\linebreak动量源(ZAMS)的单色和各向同性光子发射。我们研究了逃逸到无穷远的光子的逃逸几率,并研究了逃逸光子的能量位移,它可以表示为源半径和黑洞自旋的函数。我们研究了一般的源半径和黑洞自旋的情况,但我们特别注意的近视界(近)极值克尔((近)NHEK)的情况。我们使用一种更有效的方法再现了相关的数值结果,并得到了新的(近)极值情况下的解析结果。主要结果是:在(近)极值Kerr黑洞的NHEK区,ZAMS的逃逸几率趋于$\frac{7}{24}\approx 29.17\%$,与NHEK半径无关;在近NHEK区域中的光子壳层(IPS)的最内侧,ZAMS的逃逸概率趋于\begin{equation} \frac{5}{12} -\frac{1}{\sqrt{7}} + \frac{2}{\sqrt{7}π}\arctan\frac{1}{\sqrt{7}}\approx12.57\% . \nonumber \end{equation}。结果表明,即使ZAMS是在一个高自旋克尔黑洞的近视界喉道的最深区域,只要ZAMS在IPS之外。然而,在无穷远处逃逸光子的能量都发生了红移,但原则上仍然可见。

英文摘要:

We revisit monochromatic and isotropic photon emissions from the zero-angular\linebreak-momentum sources (ZAMSs) near a Kerr black hole. We investigate the escape probability of the photons that can reach to infinity and study the energy shifts of these escaping photons, which could be expressed as the functions of the source radius and the black hole spin. We study the cases for generic source radius and black hole spin, but we pay special attention to the near-horizon (near-)extremal Kerr ((near-)NHEK) cases. We reproduce the relevant numerical results using a more efficient method and get new analytical results for (near-)extremal cases. The main non-trivial results are: in the NHEK region of a (near-)extremal Kerr black hole, the escape probability for a ZAMS tends to $\frac{7}{24}\approx 29.17\%$, independent of the NHEK radius; at the innermost of the photon shell (IPS) in the near-NHEK region, the escape probability for a ZAMS tends to \begin{equation} \frac{5}{12} -\frac{1}{\sqrt{7}} + \frac{2}{\sqrt{7}π}\arctan\frac{1}{\sqrt{7}}\approx12.57\% . \nonumber \end{equation} The results show that the photon escape probability remains a relatively large nonzero value even though the ZAMS is in the deepest region of a near-horizon throat of a high spin Kerr black hole, as long as the ZAMS is outside the IPS. The energies of the escaping photons at infinity, however, are all redshifted but still visible in principle.

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