Null geodesics and shadow of a rotating black hole in extended Chern-Simons modified gravity

Abstract

The Chern-Simons modification to general relativity in four dimensions consists of adding to the Einstein-Hilbert term a scalar field that couples to the first class Pontryagin density. In this theory, which has attracted considerable attention recently, the Schwarzschild metric persists as an exact solution, and this is why this model resists several observational constraints. In contrast, the spinning black hole solution of the theory is not given by the Kerr metric but by a modification of it, so far only known for slow rotation and small coupling constant. In the present paper, we show that, in this approximation, the null geodesic equation can be integrated, and this allows us to investigate the shadow cast by a black hole. We discuss how, in addition to the angular momentum of the solution, the coupling to the Chern-Simons term deforms the shape of the shadow.

Shadow of a rotating braneworld black hole

“…Rotating black holes present apparent shapes or shadows with an optical deformation due to the spin [19,20], instead of being circles as in the case of non-rotating ones. This topic has been reexamined by several authors in the last few years [17,[21][22][23][24][25][26][27][28], with the expectation that the direct observation of black holes will be possible in the near future [28]; therefore the study of the shadows will be useful for measuring the properties of astrophysical black holes. Optical properties of rotating braneworld black holes were studied by Schee and Stuchlik [29].…”

On the shadow of rotating traversable wormholes

“…Motivated by present observational missions [5], the shadows of a variety of black holes were studied, both in general relativity and alternative theories of gravity [6][7][8][9][10][11][12][13][14][15][16]. The specific features of the images can be used to extract information about the physical properties of the compact objects, and to a e-mail: gyulchev@phys.uni-sofia.bg b e-mail: pnedkova@phys.uni-sofia.bg c e-mail: yazad@phys.uni-sofia.bg differentiate between gravitational theories [17][18][19].…”

Testing Einstein-dilaton-Gauss-Bonnet gravity with the reflection spectrum of accreting black holes

“…Tests with electromagnetic radiation include, but are not limited to, the study of the thermal spectrum of thin accretion disks [7][8][9][10], the analysis of the reflection spectrum of thin disks [11][12][13][14], the measurements of the frequencies of quasiperiodic oscillations [15][16][17][18], and the possible future detection of black hole shadows [19][20][21][22][23][24][25]. Among these techniques, x-ray reflection spectroscopy is the only one that can be already used to test astrophysical black holes and promise to be able to provide stringent constraints with the next generation of x-ray facilities [26][27][28].…”