Remarks on the light ring images and the optical appearance of hairy black holes in Einstein-Maxwell-dilaton gravity

Abstract

The behaviors of null geodesics in the spherical symmetric black holes in Einstein-Maxwell-dilaton (EMD) theory with coupling function $f(\Phi )=e^{-2\alpha \Phi }$ are meticulously analyzed. We investigate the effects of coupling constant $\alpha$ on the effective potential of photon trajectories within three ranges, namely $0<\alpha <1$, $\alpha =1$ and $\alpha >1$. We find that the thicknesses of lensing and photon rings are smaller at larger $\alpha$ and fixed electric charge in the unit of mass $q$, whereas they are larger at fixed $\alpha$ and larger $q$. This behavior can be described by using the angular Lyapunov exponent $\gamma$ in the vicinity of the critical curve. Remarkably, the behaviors of photon trajectories are found to be more interesting when $\alpha >1$. Namely, the radius of the black hole shadow $R_{\text{s}}$ becomes to be smaller than the photon sphere radius $r_{\text{ph}}$ when $\alpha >1$ and $q>q^{\ast }$. Moreover, $R_{\text{s}}$ goes to zero as $q$ saturates the extremal limit, beyond which the photon orbit becomes absent. Furthermore, we construct the optical appearance of black holes surrounded by optically and geometrically thin accretion disk with three cases of Gralla-Lupsasca-Marrone (GLM) emission profile. Our results indicate that the observed flux originating from the lensing and photon rings exhibits suppression as $\alpha$ increases, while it undergoes amplification with the increasing parameter $q$.

v3: Accretion disk profile has been changed to the Gralla-Lupsasca-Marrone (GLM) emission profile. Appendix B: Null Energy Condition and Focusing Theorem has been added. The angular Lyapunov exponent is applied to discuss the thickness of the photon ring

References in corpus (41)

• 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. 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
• First Sagittarius A* Event Horizon Telescope Results. VI: Testing the Black Hole Metric
• Black Hole Shadows, Photon Rings, and Lensing Rings
• First Sagittarius A* Event Horizon Telescope Results. V. Testing Astrophysical Models of the Galactic Center Black Hole
• Measurement of the Kerr Spin Parameter by Observation of a Compact Object's Shadow
• First Sagittarius A* Event Horizon Telescope Results. III: Imaging of the Galactic Center Supermassive Black Hole
• Light ring stability in ultra-compact objects
• First Sagittarius A* Event Horizon Telescope Results. II. EHT and Multi-wavelength Observations, Data Processing, and Calibration
• First Sagittarius A* Event Horizon Telescope Results. IV. Variability, Morphology, and Black Hole Mass
• A new method for shadow calculations: application to parameterised axisymmetric black holes
• Black holes with scalar hair in light of the Event Horizon Telescope
• Shadow of five-dimensional rotating Myers-Perry black hole
• The Shadow of a Spherically Accreting Black Hole
• Lensing by Kerr Black Holes
• Photon Ring and Observational Appearance of a Hairy Black Hole
• Topological Charge and Black Hole Photon Spheres
• Imaging compact boson stars with hot-spots and thin accretion disks
• Shadows and photon rings of regular black holes and geonic horizonless compact objects
• Images and photon ring signatures of thick disks around black holes
• Holographic Complexity Equals Which Action?
• Upper bound on the radii of black-hole photonspheres
• Investigating shadow images and rings of the charged Horndeski black hole illuminated by various thin accretions
• Rings and images of Horndeski hairy black hole illuminated by various thin accretions
• Observational properties of relativistic fluid spheres with thin accretion disks
• On the Size of a Black Hole: The Schwarzschild is the Biggest
• Strong gravitational lensing across dilaton anti-de Sitter black hole
• Particle motion and gravitational lensing in the metric of a dilaton black hole in a de Sitter universe
• Light Ring behind Wormhole Throat: Geodesics, Images and Shadows
• Optical appearance of black holes surrounded by a dark matter halo
• Does the shape of the shadow of a black hole depend on motional status of an observer?
• Thin accretion disks and charged rotating dilaton black holes
• Motion of Test Particles around a Charged Dilatonic Black Hole
• Shadows of rotating Einstein-Maxwell-dilaton black holes surrounded by a plasma
• Scalarization of planar anti de Sitter charged black holes in Einstein-Maxwell-Scalar theory
• Bound on photon circular orbits in general relativity and beyond

Cited by in corpus (1)

• Shadows and Observational Images of a Schwarzschild-like Black Hole Surrounded by a Dehnen-type Dark Matter Halo