Spacetime Measurements with the Photon Ring

Abstract

We explore the universal symmetries of the black hole photon ring in a wide range of non-Kerr spacetimes, including the Kerr-Newman, Kerr-Sen, Kerr-Bardeen, and Kerr-Hayward metrics. The demagnification exponent ($\gamma$) controls the size and flux scaling of higher-order images, which appear in the photon ring, the time delay ($\tau$) determines the timing of their appearance, and the rotation parameter ($\delta$) relates their relative orientations on the image plane. Our investigation reveals that these critical parameters respond distinctly to variations in black hole spin, generalized charge, and observer inclination, establishing them as complementary probes of spacetime geometry: $\gamma$ is predominantly influenced by charge and spin, $\tau$ is strongly affected by inclination, especially for near-extremal black holes, and $\delta$ is highly sensitive to spin. Notably, we find that the time delay provides an independent constraint on shadow size for polar observers, while the rotation parameter facilitates metric-independent spin measurements. Specifically, for Kerr black holes, the total variation in $\gamma$, $\tau$, and $\delta$ across all possible inclinations and spins is $\lesssim 20\%$, $\lesssim 10\%$, and $\lesssim 60\%$, respectively. By contrast, the Kerr shadow radius varies by only $\lesssim 8\%$. A future joint measurement of these critical parameters -- along with the black hole shadow size -- will enable precise spacetime characterization, including measurements of the spin, inclination, and generalized charge.

15 pages and 8 figures. Matches with the published version

References in corpus (54)

• First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
• First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way
• First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole
• Horizon-scale tests of gravity theories and fundamental physics from the Event Horizon Telescope image of Sagittarius A${}^{\ast }$
• First Sagittarius A* Event Horizon Telescope Results. VI: Testing the Black Hole Metric
• Black Hole Shadows, Photon Rings, and Lensing Rings
• Rotating regular black holes
• The Black-Hole Mass in M87 from Gemini/NIFS Adaptive Optics Observations
• Measurement of the Kerr Spin Parameter by Observation of a Compact Object's Shadow
• Detection of orbital motions near the last stable circular orbit of the massive black hole SgrA*
• Light ring stability in ultra-compact objects
• Universal Interferometric Signatures of a Black Hole's Photon Ring
• Constraints on black-hole charges with the 2017 EHT observations of M87*
• Gravitational Test Beyond the First Post-Newtonian Order with the Shadow of the M87 Black Hole
• A new method for shadow calculations: application to parameterised axisymmetric black holes
• The Structure and Dynamics of the Sub-parsec Scale Jet in M87 Based on 50 VLBA Observations Over 17 Years at 43 GHz
• Regular Black Hole Metric with Three Constants of Motion
• The Shadow of a Spherically Accreting Black Hole
• Photon Rings around Kerr and Kerr-like Black Holes
• Lensing by Kerr Black Holes
• Black Hole Parameter Estimation from Its Shadow
• Constraining the spin and the deformation parameters from the black hole shadow
• Chaotic lensing around boson stars and Kerr black holes with scalar hair
• Key Science Goals for the Next-Generation Event Horizon Telescope
• Universal Polarimetric Signatures of the Black Hole Photon Ring
• Testing Rotating Regular Metrics as Candidates for Astrophysical Black Holes
• Binary black hole shadows, chaotic scattering and the Cantor set
• Testing Rotating Regular Metrics with EHT Results of Sgr A*
• Images and photon ring signatures of thick disks around black holes
• Photon rings of spherically symmetric black holes and robust tests of non-Kerr metrics
• Shadows of parametrized axially symmetric black holes allowing for separation of variables
• Photon Ring Autocorrelations
• On the Observable Shape of Black Hole Photon Rings
• Black Hole Images as Tests of General Relativity: Effects of Spacetime Geometry
• The Black Hole Explorer: Motivation and Vision
• Photon ring test of the Kerr hypothesis: Variation in the ring shape
• Particle motion near high-spin black holes
• A Parametric model for the shapes of black-hole shadows in non-Kerr spacetimes
• Distinguishing gravitational and emission physics in black-hole imaging: spherical symmetry
• Photon rings as tests for alternative spherically symmetric geometries with thin accretion disks
• Black Hole Images as Tests of General Relativity: Effects of Plasma Physics
• The modification of photon trapping orbits as a diagnostic of non-Kerr spacetimes
• Measuring the shape of a black hole photon ring
• Prediction for the interferometric shape of the first black hole photon ring
• Black Hole Photon Rings Beyond General Relativity
• The Black Hole Explorer: Photon Ring Science, Detection and Shape Measurement
• Visibility of Black Hole Shadows in Low-luminosity AGN
• Demonstrating Photon Ring Existence with Single-Baseline Polarimetry
• Is a black hole shadow a reliable test of the no-hair theorem?
• Chaotic photon orbits and shadows of a non-Kerr object described by the Hartle-Thorne spacetime
• The Black Hole Explorer: Using the Photon Ring to Visualize Spacetime Around the Black Hole
• Photon Ring Interferometric Signatures Beyond The Universal Regime
• Fractal signatures of non-Kerr spacetimes in the shadow of light-ring bifurcations
• The Japanese Vision for the Black Hole Explorer Mission

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• Revisiting The Gravitational Mirroring In Presence of Compact Objects
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