Lensing by Kerr Black Holes

Abstract

Interpreting horizon-scale observations of astrophysical black holes demands a general understanding of null geodesics in the Kerr spacetime. These may be divided into two classes: "direct" rays that primarily determine the observational appearance of a given source, and highly bent rays that produce a nested sequence of exponentially demagnified images of the main emission: the so-called "photon ring". We develop heuristics that characterize the direct rays and study the highly bent geodesics analytically. We define three critical parameters $\gamma$, $\delta$, and $\tau$ that respectively control the demagnification, rotation, and time delay of successive images of the source, thereby providing an analytic theory of the photon ring. These observable parameters encode universal effects of general relativity, independent of the details of the emitting matter.

28 pages, 9 figures. v2: minor edits, matches published version

References in corpus (11)

• First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
• First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole
• First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole
• First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring
• First M87 Event Horizon Telescope Results. II. Array and Instrumentation
• First M87 Event Horizon Telescope Results. III. Data Processing and Calibration
• Black Hole Shadows, Photon Rings, and Lensing Rings
• Quasinormal-mode spectrum of Kerr black holes and its geometric interpretation
• Gravitational Lensing by Spinning Black Holes in Astrophysics, and in the Movie Interstellar
• Black hole Spin Measurement Based on Time-domain VLBI Observations of Infalling Gas Cloud
• Light Echoes in Kerr Geometry: A Source of High Frequency QPOs from Random X-ray Bursts

Cited by in corpus (2)

• Measuring the shape of a black hole photon ring
• On the approximation of the black hole shadow with a simple polar curve