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General Relativity and Quantum Cosmology, gr-qc
Abstract:
Black hole (BH) shadows in dynamical binary BHs (BBHs) have been produced via
ray-tracing techniques on top of expensive fully non-linear numerical
relativity simulations. We show that the main features of these shadows are
captured by a simple quasi-static resolution of the photon orbits on top of the
static double-Schwarzschild family of solutions. Whilst the latter contains a
conical singularity between the line separating the two BHs, this produces no
major observable effect on the shadows, by virtue of the underlying cylindrical
symmetry of the problem. This symmetry is also present in the stationary BBH
solution comprising two Kerr BHs separated by a massless strut. We produce
images of the shadows of the exact stationary co-rotating (even) and
counter-rotating (odd) stationary BBH configurations. This allow us to assess
the impact on the binary shadows of the intrinsic spin of the BHs, contrasting
it with the effect of the orbital angular momentum.
