Shadows and lensing of black holes immersed in strong magnetic fields

Abstract

We investigate the null geodesic flow and in particular the light rings (LRs), fundamental photon orbits (FPOs) and shadows of a black hole (BH) immersed in a strong, uniform magnetic field, described by the Schwarzschilld-Melvin electrovacuum solution. The empty Melvin magnetic Universe contains a tube of planar LRs. Including a BH, for weak magnetic fields, the shadow becomes oblate, whereas the intrinsic horizon geometry becomes prolate. For strong magnetic fields (over-critical solutions), there are no LRs outside the BH horizon, a result explained using topological arguments. This feature, together with the light confining structure of the Melvin Universe yields panoramic shadows, seen (almost) all around the equator of the observer's sky. Despite the lack of LRs, there are FPOs, including polar planar ones, which define the shadow edge. We also observe and discuss chaotic lensing, including in the empty Melvin Universe, and multiple disconnected shadows.

Kerr Black hole shadows in Melvin magnetic field with stable photon orbits

“…We firstly studied Melvin-Schwarzschild black hole (the rotation parameter a = 0) shadows with different magnetic field parameters B, and also found the shadow becomes more oblate as B increases, which is consistent with that obtained in ref. [66]. But after further analysis, we find the black hole shadow elongates in the horizontal direction with magnetic field parameter B, but not in the vertical direction.…”

“…Therefore, chaotic motion of test particle appears in Melvin-Schwarzschild black hole spacetime [65]. Recently, H. C. D. Lima Junior et al investigated the shadow and chaotic lensing of Melvin-Schwarzschild black hole, and found the shadow becomes oblate for weak magnetic field [66]. It is natural to ask what new effects in black hole shadow arising from the spin parameter for a rotating black hole immersed in uniform magnetic field.…”

Rotating black holes with an anisotropic matter field

“…Due to this property, the shape of the capturecross-section by light is transformed into an asymmetric one. An interesting astrophysical phenomenon is that the shadow of a rotating black hole has the asymmetric bright side due to this property [43,44,45,46,47,48,49,50,51,52,53,54].…”

Compact objects in quadratic Palatini gravity generated by a free scalar field

“…The collection of gravitational waves measured so far [4][5][6] brings in new information that allows to explore in some detail key aspects of compact objects that go beyond the paradigm set by black holes (BHs) [7][8][9]. Moreover, the view provided by advanced numerical simulations and the very large baseline interferometry techniques that enabled the reconstruction of the shadow of the supermassive object in the center of M87 [10] stands now as a solid complementary source of information for the study of critical light curves and light rings [11][12][13][14][15][16][17], which are crucial elements to tell apart BHs from other exotic compact objects.…”