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arXiv 2303.02111gr-qcastro-ph.HEhep-th
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广义相对论之外的黑洞光子环

Black Hole Photon Rings Beyond General Relativity

Seppe Staelens, Daniel R. Mayerson, Fabio Bacchini, Bart Ripperda, Lorenzo Küchler

AI总结:

研究黑洞成像光子环能否区分Kerr黑洞与替代黑洞,计算三种替代黑洞光子环发现需大偏离和大倾角才能改变形状,而Lyapunov指数对偏离更敏感,为未来观测奠定基础。

摘要:

我们研究黑洞成像中的光子环观测是否能够区分广义相对论中的Kerr黑洞和偏离Kerr的替代黑洞。光子环的某些特性已被论证为甚长基线干涉测量(VLBI)黑洞观测中稳健的观测量,携带着底层时空的印记。光子环形状及其Lyapunov指数(编码连续光子亚环的变窄)是底层几何的详细探针;对其测量已被论证可为广义相对论和Kerr度规提供强有力的零检验。然而,一个更复杂的问题是,此类对光子环特性的观测能否区分Kerr黑洞和替代黑洞。我们通过计算Johannsen、Rasheed-Larsen和Manko-Novikov黑洞的光子环,为这一问题提供了初步解答。我们发现,要获得光子环形状上可测量的差异,需要相对于Kerr存在大偏离以及大观测者倾角。换言之,即使在低倾角下对于偏离Kerr的黑洞,Kerr光子环形状似乎也是普适形状。另一方面,对于偏离Kerr度规的情况,Lyapunov指数显示出更显著的变异。我们的分析为确定未来观测任务可能探测到的光子环中偏离Kerr时空的情况奠定了基础。

英文摘要:

We investigate whether photon ring observations in black hole imaging are able to distinguish between the Kerr black hole in general relativity and alternative black holes that deviate from Kerr. Certain aspects of photon rings have been argued to be robust observables in Very-Long-Baseline Interferometry (VLBI) black hole observations which carry imprints of the underlying spacetime. The photon ring shape, as well as its Lyapunov exponent (which encodes the narrowing of successive photon subrings), are detailed probes of the underlying geometry; measurements thereof have been argued to provide a strong null test of general relativity and the Kerr metric. However, a more complicated question is whether such observations of the photon ring properties can distinguish between Kerr and alternative black holes. We provide a first answer to this question by calculating photon rings of the Johannsen, Rasheed-Larsen, and Manko-Novikov black holes. We find that large deviations from Kerr and large observer inclinations are needed to obtain measurable differences in the photon ring shape. In other words, the Kerr photon ring shape appears to be the universal shape even for deviating black holes at low inclinations. On the other hand, the Lyapunov exponent shows more marked variations for deviations from the Kerr metric. Our analysis lays out the groundwork to determine deviations from the Kerr spacetime in photon rings that are potentially detectable by future observing missions.

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