PHOTON RINGS AROUND KERR AND KERR-LIKE BLACK HOLES
PHOTON RINGS AROUND KERR AND KERR-LIKE BLACK HOLES
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DOI：
10.1088/0004-637x/777/2/170
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发表时间：
2013-10
期刊：
影响因子：
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通讯作者：
T. Johannsen
中科院分区：
文献类型：
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作者：
T. Johannsen
非常长的基线干涉观测已经解决了我们银河系和M87中心超大质量黑洞周围只有几个史瓦西半径尺度的结构。在不久的将来，这种观测有望将这些黑洞的阴影与围绕其阴影的明亮而狭窄的环一起成像。对于克尔黑洞来说，这个光子环的形状几乎是圆形的，除非黑洞旋转得非常快。然而，天体物理学黑洞是否真的被克尔度规描述为无毛定理，仍然是一个未经检验的假设。对于不同于克尔黑洞的黑洞，光子环已经在数值上被证明对于小到中等自旋是不对称的。本文计算了一种新的Kerr类度规所描述的黑洞周围光子环形状的半解析表达式。我表明，在这个时空中的光子环受到两种类型的偏离克尔度规，这可能会导致环的形状是高度不对称的。我认为，环的不对称性是一个潜在的违反无毛定理的直接措施，这两种类型的偏差可以独立检测，如果黑洞的质量和距离是已知的。此外，还得到了Kerr黑洞和类Kerr黑洞周围光子环的直径、位移和不对称性的近似表达式。
Very long baseline interferometric observations have resolved structure on scales of only a few Schwarzschild radii around the supermassive black holes at the centers of our Galaxy and M87. In the near future, such observations are expected to image the shadows of these black holes together with a bright and narrow ring surrounding their shadows. For a Kerr black hole, the shape of this photon ring is nearly circular unless the black hole spins very rapidly. Whether or not, however, astrophysical black holes are truly described by the Kerr metric as encapsulated in the no-hair theorem still remains an untested assumption. For black holes that differ from Kerr black holes, photon rings have been shown numerically to be asymmetric for small to intermediate spins. In this paper, I calculate semi-analytic expressions of the shapes of photon rings around black holes described by a new Kerr-like metric which is valid for all spins. I show that photon rings in this spacetime are affected by two types of deviations from the Kerr metric which can cause the ring shape to be highly asymmetric. I argue that the ring asymmetry is a direct measure of a potential violation of the no-hair theorem and that both types of deviations can be detected independently if the mass and distance of the black hole are known. In addition, I obtain approximate expressions of the diameters, displacements, and asymmetries of photon rings around Kerr and Kerr-like black holes.