133 citations · 799 across the 14 of their papers we have counts for
14 papers
Polarized Equatorial Emission around Kerr Black Holes with Synchronized Scalar Hair. I. Direct images
Valentin O. Deliyski, Galin N. Gyulchev, Daniela D. Doneva +2
We investigate the polarization properties of the direct images of a geometrically and optically thin accretion disk around fully self-consistent models of rotating Kerr black hole…
Images of the Thin Accretion Disk Around Kerr Black Holes coupled to time periodic scalar fields
Galin N. Gyulchev, Daniela D. Doneva, Valentin O. Deliyski +2
We investigate the orbital structure and observable appearance of rotating Kerr black holes endowed with synchronized scalar hair described by two time-periodic scalar fields with…
Testing disformal non-circular deformation of Kerr black holes with LISA
Eugeny Babichev, Christos Charmousis, Daniela D. Doneva +2
There is strong observational evidence that almost every large galaxy has a supermassive black hole at its center. It is of fundamental importance to know whether such black holes…
Shadows of rotating hairy Kerr black holes coupled to time periodic scalar fields with non-flat target space
Galin N. Gyulchev, Ayush Roy, Lucas G. Collodel +3
We study the shadows cast by rotating hairy black holes with two non-trivial time-periodic scalar fields having a non-flat Gaussian curvature of the target space spanned by the sca…
Observational signatures of strongly naked singularities: image of the thin accretion disk
Galin Gyulchev, Jutta Kunz, Petya Nedkova +2
We study the optical appearance of a thin accretion disk around the strongly naked static Janis-Newman-Winicour singularity. The solution does not possess a photon sphere, which re…
Image of the Janis-Newman-Winicour naked singularity with a thin accretion disk
Galin Gyulchev, Petya Nedkova, Tsvetan Vetsov +1
We study the optical appearance and the apparent radiation flux of a thin accretion disk around the static Janis-Newman-Winicour naked singularity. We confine ourselves to the astr…
Distinguishing rotating naked singularities from Kerr-like wormholes by their deflection angles of massive particles
Kimet Jusufi, Ayan Banerjee, Galin Gyulchev +1
We study the gravitational deflection of relativistic massive particles by Janis-Newman-Winicour (JNW) spacetimes (also known as a rotating source with a surface-like naked singula…
Weak Gravitational lensing by phantom black holes and phantom wormholes using the Gauss-Bonnet theorem
Ali Övgün, Galin Gyulchev, Kimet Jusufi
In this paper, we study the deflection of light by a class of phantom black hole and wormhole solutions in the weak limit approximation. More specifically, in the first part of thi…
On the shadow of rotating traversable wormholes
Galin Gyulchev, Petya Nedkova, Vassil Tinchev +1
We revisit the shadow of rotating traversable wormholes discussing the role of the wormhole throat in the shadow formation. For certain classes of wormholes the throat serves as a…
Shadows of Black Holes in Vector-Tensor Galileons Modified Gravity
Tsvetan Vetsov, Galin Gyulchev, Stoytcho Yazadjiev
We study the shadows of disformal black holes in vector-tensor Galileons modified gravity. Our analysis shows that the apparent image of the black hole in the observer's sky is non…
Gravitational Lensing by Phantom Black holes
Galin N. Gyulchev, Ivan Zh. Stefanov
In some models dark energy is described by phantom scalar fields (scalar fields with "wrong" sign of the kinetic term in the lagrangian). In the current paper we study the effect o…
Analytical Kerr-Sen Dilaton-Axion Black Hole Lensing in the Weak Deflection Limit
Galin N. Gyulchev, Stoytcho S. Yazadjiev
We investigate analytically gravitational lensing by charged, stationary, axially symmetric Kerr-Sen dilaton-axion black hole in the weak deflection limit. Approximate solutions to…
Gravitational Lensing by Rotating Naked Singularities
Galin N. Gyulchev, Stoytcho S. Yazadjiev
We model massive compact objects in galactic nuclei as stationary, axially-symmetric naked singularities in the Einstein-massless scalar field theory and study the resulting gravit…
Kerr-Sen dilaton-axion black hole lensing in the strong deflection limit
Galin N. Gyulchev, Stoytcho S. Yazadjiev
In the present work we study numerically quasi-equatorial lensing by the charged, stationary, axially-symmetric Kerr-Sen dilaton-axion black hole in the strong deflection limit. In…