Exploring Nonlinear Electrodynamics Theories: Shadows of Regular Black Holes and Horizonless Ultra-Compact Objects

Abstract

In the Einstein-Maxwell theory with nonlinear electrodynamics (NED) fields, the singularity problem in general relativity is potentially resolved, leading to regular black hole solutions. In NED theories, photons follow null geodesics of an effective geometry that differs from the spacetime geometry itself. This raises an important question: Do NED fields produce unique observational signatures in the electromagnetic spectrum that can test regular black holes and NED theories? We analyze the shadows of two NED-charged regular black holes and their horizonless ultracompact objects (HUCOs) under two accretion models, comparing them with Schwarzschild black holes, focusing on shadow size, central brightness depression, and photon ring characteristics. Our results identify distinctive NED signatures that could be observable by the EHT, providing empirical evidence of NED fields and potentially ruling out previously considered viable candidates for astrophysical black holes models based on shadow measurements. Notably, NED-charged HUCOs generally exhibit only one $\text{unstable}$ photon ring, thus avoiding the dynamical instability associated with stable photon rings and challenging the idea that objects with photon rings must be black holes.

27 Pages, 18 figures and 3 tables. Published in PRD

References in corpus (24)

• 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. V. Physical Origin of the Asymmetric Ring
• 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
• Construction of Regular Black Holes in General Relativity
• Light ring stability in ultra-compact objects
• Constraints on black-hole charges with the 2017 EHT observations of M87*
• Light rings as observational evidence for event horizons: long-lived modes, ergoregions and nonlinear instabilities of ultracompact objects
• The Shadow of a Spherically Accreting Black Hole
• Thin accretion disks in stationary axisymmetric wormhole spacetimes
• Evidence for vacuum birefringence from the first optical polarimetry measurement of the isolated neutron star RX\, J1856.5$-$3754
• A code to compute the emission of thin accretion disks in non-Kerr space-times and test the nature of black hole candidates
• Strong deflection limit of black hole gravitational lensing with arbitrary source distances
• Testing Rotating Regular Metrics as Candidates for Astrophysical Black Holes
• Testing Rotating Regular Metrics with EHT Results of Sgr A*
• First M87 Event Horizon Telescope Results. IX. Detection of Near-horizon Circular Polarization
• Comment on "Construction of regular black holes in general relativity"
• Relaxations of perturbations of spacetimes in general relativity coupled to nonlinear electrodynamics
• Singularity-free gravitational collapse and asymptotic safety
• Distinguishing gravitational and emission physics in black-hole imaging: spherical symmetry
• Regular Black Holes: Towards a New Paradigm of Gravitational Collapse
• Can a light ray distinguish charge of a black hole in nonlinear electrodynamics?