Prediction for the interferometric shape of the first black hole photon ring

Abstract

Black hole images are theoretically predicted (under mild astrophysical assumptions) to display a stack of lensed "photon rings" that carry information about the underlying spacetime geometry. Despite vigorous efforts, no such ring has been observationally resolved thus far. However, planning is now actively under way for space missions targeting the first (and possibly the second) photon rings of the supermassive black holes M87* and Sgr A*. In this work, we study interferometric photon ring signatures in time-averaged images of Kerr black holes surrounded by different astrophysical profiles. We focus on the first, most easily accessible photon ring, which has a larger width-to-diameter ratio than subsequent rings and whose image consequently lacks a sharply defined diameter. Nonetheless, we show that it does admit a precise angle-dependent diameter in visibility space, for which the Kerr metric predicts a specific functional form that tracks the critical curve. We find that a measurement of this interferometric ring diameter is possible for most astrophysical profiles, paving the way for precision tests of strong-field general relativity via near-future observations of the first photon ring.

16 pages, 6 figures. V2: Minor changes to match the published version

References in corpus (16)

• 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
• First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring
• Black Hole Shadows, Photon Rings, and Lensing Rings
• The Shadow of a Spherically Accreting Black Hole
• Lensing by Kerr Black Holes
• Observing the Inner Shadow of a Black Hole: A Direct View of the Event Horizon
• Images and photon ring signatures of thick disks around black holes
• The Photon Ring in M87*
• Photon ring test of the Kerr hypothesis: Variation in the ring shape
• Shape of higher-order images of equatorial emission rings around a Schwarzschild black hole: Analytical description with polar curves
• Adaptive Analytical Ray Tracing of Black Hole Photon Rings
• Measuring the shape of a black hole photon ring
• Black Hole Photon Rings Beyond General Relativity
• How narrow is the M87* ring? II. A new geometric model

Cited by in corpus (17)

• The Black Hole Explorer: Motivation and Vision
• Photon rings as tests for alternative spherically symmetric geometries with thin accretion disks
• Optical appearance of black holes surrounded by a dark matter halo
• The Black Hole Explorer: Photon Ring Science, Detection and Shape Measurement
• A Lensing-Band Approach to Spacetime Constraints
• Black hole photon ring beyond General Relativity: an integrable parametrization
• Multi-Frequency Models of Black Hole Photon Rings from Low-Luminosity Accretion Disks
• Inferring Black Hole Spin from Interferometric Measurements of the First Photon Ring: A Geometric Approach
• Spacetime Measurements with the Photon Ring
• Gravity versus astrophysics in black hole images and photon rings: Equatorial emissions and spherically symmetric space-times
• Photon Ring Interferometric Signatures Beyond The Universal Regime
• Photon ring polarimetry with next-generation black hole imaging I. M87*
• Assessing the impact of instrument noise and astrophysical fluctuations on measurements of the first black hole photon ring
• Probing $H_0$ and resolving AGN disks with ultrafast photon counters
• Exploring black holes with multiple photon spheres by interferometric signatures
• Probing Lorentz-violating effects via precession and accretion disk images in a rotating bumblebee spacetime
• Orbit design for mitigating interstellar scattering effects in Earth-space VLBI observations of Sgr A*