Universal Properties of Light Rings for Stationary Axisymmetric Spacetimes.
Universal Properties of Light Rings for Stationary Axisymmetric Spacetimes.
复制标题
DOI：
10.1103/physrevd.103.104031
复制
发表时间：
2020-11
期刊：
影响因子：
--
通讯作者：
Minyong Guo;Sijie Gao
中科院分区：
文献类型：
--
作者：
Minyong Guo;Sijie Gao
光环在引力波观测和黑洞照片中起着重要的作用。在这封信中，我们调查的一般特点，在平稳的，轴对称的，渐近平坦的时空有或没有地平线的LR。对于一个非极值黑洞，我们明确地表明，总是存在至少两个径向不稳定的LR在赤道平面上相反的方向传播。对于极端黑洞，我们证明了至少存在一个逆行LR。我们的方法也适用于水平时空，我们证明了在赤道平面上总是存在偶数个LR，其中最外面的一个在径向上是不稳定的。在我们的证明中只使用了一些自然的和一般的假设。结果适用于广义相对论以及大多数修正的引力理论。在这个问题上，与以前的作品相比，我们获得了更强大，更清晰的结果，一个更直接的方法。
Light rings (LRs) play an important role in gravitational wave observations and black hole photographs. In this letter, we investigate general features of LRs in stationary, axisymmetric, asymptotically flat spacetimes with or without horizons. For a nonextremal black hole, we show explicitly that there always exist at least two radially unstable LRs propagating in opposite directions on the equatorial plane. For an extremal black hole, we show that there exists at least one retrograde LR. Our method also applies to horizonless spacetimes and we prove that there always exist even number of LRs on the equatorial plane, where the outermost one is unstable in the radial direction. Only some natural and generic assumptions are used in our proof. The results are applicable to general relativity as well as most modified theories of gravity. In contrast to previous works on this issue, we obtain stronger and clearer results with a much more straightforward approach.