In this work, we study the black hole light echoes in terms of the two-photon autocorrelation and explore their connection with the quasinormal modes. It is shown that the above time-domain phenomenon can be analyzed by utilizing the well-known frequency-domain relations between the quasinormal modes and characteristic parameters of null geodesics. We found that the time-domain correlator, obtained by the inverse Fourier transform, naturally acquires the echo feature, which can be attributed to a collective effect of the asymptotic poles through a weighted summation of the squared modulus of the relevant Green's functions. Specifically, the contour integral leads to a summation taking over both the overtone index and angular momentum. Moreover, the dominant contributions to the light echoes are from those in the eikonal limit, consistent with the existing findings using the geometric-optics arguments. For the Schwarzschild black holes, we demonstrate the results numerically by considering a transient spherical light source. Also, for the Kerr spacetimes, we point out a potential difference between the resulting light echoes using the geometric-optics approach and those obtained by the black hole perturbation theory. Possible astrophysical implications of the present study are addressed.
Rotating black holes surrounded by PFDM in STVG: Shadows and eikonal quasinormal modes
Shanghai University（上海大学）；Fuzhou University（福州大学）；National University of Uzbekistan（乌兹别克斯坦国立大学）；Kimyo International University in Tashkent（塔什干基莫国际大学）；Tashkent State Technical University（塔什干国立技术大学）
A First-Order Eikonal Framework for Quasinormal Modes, Shadows, Strong Lensing, and Grey-Body Factors in a Scalarized Black-Hole Metric
University of Hradec Králové（赫拉德茨克拉洛韦大学）；National University of Uzbekistan（乌兹别克斯坦国立大学）；University of Tashkent for Applied Sciences（塔什干应用科学大学）；Tashkent State Technical University（塔什干国立技术大学）；New Uzbekistan University（新乌兹别克斯坦大学）；Tashkent International University of Education（塔什干国际教育大学）；Kimyo International University in Tashkent（塔什干基莫国际大学）；Mamun University（马蒙大学）
Scalar and Electromagnetic Perturbations around a Black Hole with a Topological Defect: Quasinormal Modes and Quasi-bound States in a Plasma Medium
Institute of Fundamental and Applied Research, National Research University TIIAME（国立研究大学TIIAME基础与应用研究所）；Kimyo International University in Tashkent（塔什干金尤国际大学）；Research Center of Astrophysics and Cosmology, Khazar University（哈扎尔大学天体物理学与宇宙学研究中心）；School of Physics, Harbin Institute of Technology（哈尔滨工业大学物理学院）；University of Tashkent for Applied Sciences（塔什干应用科学大学）；Department of Physics, Zhejiang Normal University（浙江师范大学物理系）
Analyzing Quasi-normal modes spectrum in asymptotically de Sitter black bounces and their optical appearance
Universidade Federal do Ceará (UFC)（塞阿拉联邦大学）；University of Valladolid UVA（巴利亚多利德大学）；Universidad del Bío-Bío（比奥比奥大学）；Research Centre for Theoretical Physics and Astrophysics, Institute of Physics, Silesian University in Opava（俄帕瓦西里西亚大学物理研究所理论物理与天体物理研究中心）
The detection of Quasinormal Mode of Pop III Binary Black Hole merger with final $M \sim 60M_\odot$ and $a/M \sim 0.7$ would confirm the strong gravity space-time around $\sim 2M$ which is only $\sim 1.17$ times the event horizon radius
Electrically Charged Distorted Black Holes: Thermodynamics, Particle Dynamics, and Quasinormal Signatures
The British University in Egypt（埃及英国大学）；Università di Napoli ”Federico II”（那不勒斯费德里科二世大学）；Scuola Superiore Meridionale（南方高等学院）；Istituto Nazionale di Fisica Nucleare (INFN)（意大利国家核物理研究所）
