Calculating black hole shadows: Review of analytical studies

hep-th 2026-08 conditional novelty 7.0 of 10

In modified-gravity theories, spin Hall deflection of light and gravitational waves by a spinning black hole becomes non-commuting, so a ray disperses into a blob, and black-hole spin direction can tighten causality b...

gr-qc 2026-08 accept novelty 6.0 of 10

An eternal Schwarzschild black hole with an emitting surface at r=r_m would show a bright spot inside its shadow, whose interferometric visibility decays exponentially with baseline length.

gr-qc 2026-07 conditional novelty 6.0 of 10

Using public 2017 M87* closure data, a frozen Kerr source fails an absolute adequacy test and the differential tidal-charge response fails numerical convergence, so no posterior or bound is reported.

gr-qc 2026-07 accept novelty 6.0 of 10

In the spindle-deformed Kerr black hole, null geodesics separate at O(B²) while timelike do not; the deformation shifts the ISCO, can create an OSCO, and enlarges the shadow versus Kerr.

gr-qc 2026-03 conditional novelty 6.0 of 10

For a magnetized Kerr-Bertotti-Robinson black hole, the photon-ring parameters gamma, delta, and tau all decrease compared with the unmagnetized Kerr case, weakening the self-similar stacking of higher-order images.

gr-qc 2026-02 conditional novelty 6.0 of 10

In MOG gravity, gravitational waves would make a black hole's shadow breathe in area and then wobble translationally after a time delay, signatures absent in general relativity.

gr-qc 2025-11 conditional novelty 6.0 of 10

A regular black hole spacetime sourced by a Letelier-Alencar string cloud with a rational Dagum regulator has an AdS core, finite curvature, and EHT-compatible shadows.

gr-qc 2025-11 conditional novelty 6.0 of 10

An adaptive ray-tracing and MCMC framework estimates shadow observables for arbitrary stationary metrics; applied to the Kerr–Bertotti–Robinson spacetime it yields an Sgr A* horizon-scale magnetic field of about 93 G ...

gr-qc 2025-08 conditional novelty 6.0 of 10

For the Kerr-Bertotti-Robinson black hole, the magnetic field mainly enlarges the shadow and Einstein ring while rotation mainly distorts the shadow shape, and current M87* and Sgr A* data give only weak bounds on the field.

gr-qc 2025-01 conditional novelty 6.0 of 10

Numerical ray tracing shows the toron, a massless but gravimagnetically charged exact solution, produces NUT-like lensing with a hidden region of the celestial sphere and an asymmetric shadow caused by its toroidal er...

hep-th 2024-12 conditional novelty 6.0 of 10

The worldline formalism yields a closed-form NLO plasma-induced deflection angle for power-law electron density, matching previous results where they exist.

gr-qc 2024-11 conditional novelty 6.0 of 10

For Johannsen-Psaltis spacetimes, the polar photon-ring time delay depends only on spin and shadow size, while the azimuthal shift probes the metric ratio F/N, enabling future spin and frame-dragging tests.

gr-qc 2024-11 conditional novelty 6.0 of 10

Shadows of generalized Hayward spacetimes are computed in vacuum and plasma, and EHT Sgr A* constraints favor wormholes with multi-peak effective potentials over single-peak ones.

gr-qc 2024-11 conditional novelty 6.0 of 10

The shadow contour of a Kerr-Newman black hole observed at infinity uniquely fixes (a/M, Q/M, i), while finite-distance shadows are degenerate for zero spin.

gr-qc 2026-07 conditional novelty 5.5 of 10

Weyl-coupled photons on Schwarzschild produce a polarization-split double shadow (62% edge separation at α/M²=0.75) and a parity-protected backward birefringence signal that vanishes at α=0.

gr-qc 2026-08 conditional novelty 5.0 of 10

A two-parameter regular black hole family is constructed, with an explicit nonlinear electrodynamics source, exact thermodynamic identities, and analytic shadow and plasma-lensing predictions.

gr-qc 2026-08 accept novelty 5.0 of 10

The paper proves a sufficient convexity criterion for off-shell Kerr radial mass profiles and derives first-order horizon, photon-sphere, and shadow responses for a fuzzy-dark-matter-inspired benchmark.

gr-qc 2026-07 conditional novelty 5.0 of 10

For self-similar Husain black holes, the barotropic index α controls the shadow: α<1/2 enlarges it, α>1/2 shrinks it, with a quasistatic influx criterion for the time-dependent case.

gr-qc 2026-07 conditional novelty 5.0 of 10

EHT dimensionless shadow diameters plus stellar-dynamical mass priors constrain Einasto central density to ρ₀ ≲ 10^{-11} M⊙/pc³ (1σ) for Sgr A*, with weaker bounds for M87*.

gr-qc 2026-05 unverdicted novelty 5.0 of 10

Positive/negative-mass binaries would emit gravitational waves with decreasing frequency and amplitude, and a negative-mass wormhole would cast an asymmetric shadow with richer photon-ring substructure than a black hole.

gr-qc 2026-02 conditional novelty 5.0 of 10

Stable static dark-fluid shells separating two Schwarzschild–de Sitter spacetimes exist only for m_+/m_->1 and arise at three scales, imprinting observable black-hole shadow deviations.

gr-qc 2025-08 conditional novelty 5.0 of 10

For exact asymptotically flat hairy charged black holes with a dilaton potential, the shadow radius, photon-orbit Lyapunov exponent, and scalar quasinormal frequencies are computed, showing strong coupling dependence ...

gr-qc 2025-06 conditional novelty 5.0 of 10

EHT shadow data constrain the EMCS black hole charge and scalar hair to about 0.1 and 0.01 levels, while LISA EMRI waveforms could reach 0.01 and 0.0001 levels.

gr-qc 2025-02 conditional novelty 5.0 of 10

Einsteinian cubic gravity shrinks (grows) black hole horizons for positive (negative) coupling and shifts the photon sphere enough that SgrA* shadow observations can bound the coupling to approximately 0.1.

gr-qc 2025-02 conditional novelty 5.0 of 10

Three new charged black hole spacetimes in conformal Killing gravity reproduce the Sgr A* shadow size after parameter tuning.

gr-qc 2024-11 conditional novelty 5.0 of 10

EHT shadow sizes and LIGO/Virgo/KAGRA inspiral waveforms allow only small values of the dimensionless regularity parameter ℓ in the Ghosh-Simpson-Visser regular black hole.

gr-qc 2026-07 conditional novelty 4.5 of 10

Plasma and topological defect k suppress scalar QNM frequencies and allow axial EM quasi-bound states only for homogeneous plasma below a k- and l-dependent critical frequency.

gr-qc 2026-07 conditional novelty 4.5 of 10

An exact Schwarzschild-like black hole embedded in a King dark-matter halo is obtained from Einstein’s equations and shown to enlarge the photon sphere, shadow, and thermodynamic stability region relative to vacuum.

gr-qc 2026-07 conditional novelty 4.0 of 10

A generalized-entropy black-hole model with horizon temperature fixed by entropy predicts sign-controlled ISCO, shadow, and efficiency shifts, but relies on an arbitrary exterior profile p.

gr-qc 2026-07 conditional novelty 4.0 of 10

Increasing zero-point length makes photon and ISCO orbits more compact in ADM units while heavier scalars raise oscillation frequency and suppress damping on this regular self-energy black hole.

gr-qc 2026-03 conditional novelty 4.0 of 10

Homogeneous plasma enlarges Kerr-like black-hole shadows and emission rates while inhomogeneous plasma shrinks them; astrophysical dark-matter densities leave photon orbits essentially unchanged.

gr-qc 2026-03 conditional novelty 4.0 of 10

PINLED Y^n black holes have charge-driven inward shifts of photon sphere, shadow, and ISCO, with null-geodesic observables distinguishing them from RN more clearly than timelike ones.

gr-qc 2025-10 conditional novelty 4.0 of 10

An ASG-modified Newton constant combined with a Dekel–Zhao dark matter halo yields traversable wormhole geometries whose shadow radius can be tuned to the EHT Sgr A* bound by choosing the ASG scale ξ/M ≈ 0.8–0.9.

gr-qc 2025-07 conditional novelty 4.0 of 10

Surrounding a Fan-Wang regular black hole with a Kiselev-type anisotropic fluid with omega in (-1,-1/3) modestly enlarges the horizon, photon sphere, and shadow, and EHT data constrain the fluid strength a to about 0....

gr-qc 2025-07 conditional novelty 4.0 of 10

For a Vaidya black hole with linearly growing mass, the accretion disk image's bright spot shifts radially outward with the conformal time coordinate, while the observed flux in the conformal frame remains time-independent.

gr-qc 2025-06 conditional novelty 4.0 of 10

For a static Kalb-Ramond black hole, increasing the Lorentz-breaking parameters shrinks the shadow, while plasma shrinks the shadow but brightens it, giving tentative signatures to distinguish it from Schwarzschild.

gr-qc 2025-05 reject novelty 4.0 of 10

A Godel-rotation-modified uncertainty principle is used to define a corrected black hole mass, producing enlarged horizon, shadow, and deflection with lower bounds a/M ~ 10^5 from EHT and PPN data.

gr-qc 2025-05 reject novelty 4.0 of 10

The Kalb-Ramond black hole phenomenology is mostly an extension of known results, and its shadow formula is internally inconsistent, invalidating the EHT-based constraints.

gr-qc 2025-05 reject novelty 4.0 of 10

A heuristic model claims neutrino- and boson-mediated forces would shift black hole photon spheres and shadows, with attractive forces enlarging and repulsive forces shrinking them.

gr-qc 2025-05 reject novelty 4.0 of 10

A proposed exact black hole solution in an empirical dark matter halo of NGC 4649 is internally inconsistent: the claimed metric does not satisfy the paper's own field equation for F(r).

gr-qc 2025-05 reject novelty 4.0 of 10

Two Schwarzschild-type metrics with the NGC 4649 dark matter halo profile are constructed to estimate shadow radii and derive Smarr-type thermodynamic relations, but a factor-of-3 error in the photon sphere equation a...

gr-qc 2025-04 conditional novelty 4.0 of 10

The paper computes scalar quasinormal modes of rotating Bardeen and Hayward black holes and finds they follow the eikonal null-geodesic relations, with Bardeen deviations up to about 19% from Kerr.

gr-qc 2025-02 reject novelty 4.0 of 10

A new closed-form weak deflection angle and shadow analysis for a magnetically charged NED black hole, with strong-field results that reduce to Schwarzschild after a mass redefinition.

gr-qc 2024-12 conditional novelty 4.0 of 10

Strong lensing by rotating regular black holes shifts lensing coefficients, image positions, magnifications, and time delays relative to Kerr, with M87* time delays differing by up to tens of hours while image positio...

gr-qc 2024-12 reject novelty 4.0 of 10

In F(R) gravity, the black hole shadow shift is controlled by a free perturbing function, so matching the M87* and Sgr A* shadow sizes reduces to fitting that function.

gr-qc 2024-11 conditional novelty 4.0 of 10

The authors derive a family of charged black hole metrics in f(R,T)=R+βT gravity with Lagrangian L=f0+F+αF^p, show they have curvature singularities at the origin, and use the Sgr A* shadow to place weak upper bounds ...

gr-qc 2024-11 reject novelty 3.0 of 10

The authors derive a black hole metric with a cosmological-constant-dependent effective mass and use EHT and VLBI data to put extremely weak bounds on a quantum parameter beta.