Chaotic lensing around boson stars and Kerr black holes with scalar hair

By P. Cunha, J. Grover, Carlos A. R. Herdeiro, Eugen Radu, H. R'unarsson, Alexander Wittig. 2016

136 citations recorded by the source corpus.

In a recent letter, arXiv:1509.00021, it was shown that the lensing of light around rotating boson stars and Kerr black holes with scalar hair can exhibit chaotic patterns. Since no separation of variables is known (or expected) for geodesic motion on these backgrounds, we examine the 2D effective potentials for photon trajectories, to obtain a deeper understanding of this phenomenon. We find that the emergence of stable light rings on the background spacetimes, allows the formation of "pockets" in one of the effective potentials, for open sets of impact parameters, leading to an effective trapping of some trajectories, dubbed quasi-bound orbits. We conclude that pocket formation induces chaotic scattering, although not all chaotic orbits are associated to pockets. These and other features are illustrated in a gallery of examples, obtained with a new ray-tracing code, PYHOLE, which includes tools for a simple, simultaneous visualization of the effective potential together with the spacetime trajectory, for any given point in a lensing image. An analysis of photon orbits allows us to further establish a positive correlation between photon orbits in chaotic regions and those with more than one turning point in the radial direction; we recall that the latter is not possible around Kerr black holes. Moreover, we observe that the existence of several light rings around a horizon (several fundamental orbits, including a stable one), is a central ingredient for the existence of multiple shadows of a single hairy black hole. We also exhibit the lensing and shadows by Kerr black holes with scalar hair, observed away from the equatorial plane, obtained with PYHOLE.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/6c1869a757c38cc8c20d2067cf6e3861c4ef5561

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Citations in the corpus

Shadows and strong gravitational lensing: a brief review (2018, background): “However, we remark that (in general) LRs are not necessarily connected to a shadow edge, namely if multiple unstable LRs are available, or if horizonless UCOs are considered [24,25].”
Shadows of Einstein–dilaton–Gauss–Bonnet black holes (2016, unknown): “Following [31,53], the x coordinate is defined to be directly proportional to an observation angle β along that axis: x = −R̃ β , where the perimetral radius R̃ ≡ √gφφ is computed at the observer’s position.”
Black holes with scalar hair in light of the Event Horizon Telescope (2020, background): “For an inevitably incomplete list of important studies related to the construction and identification of observational signatures of HBHs in various theories of gravity or in the presence of various different types of matter fields, see for instance [5–54].”