Motivated by M-theory compactifications, we investigate optical properties of
black holes in the Starobinsky-Bel-Robinsion gravity. Precisely, we study the
shadows and the deflection angle of light rays by non-rotating and rotating
black holes in such a novel gravity. We start by discussing the shadows of the
Schwarzschild-type solutions. As expected, we obtain perfect circular shadows
where the size decreases with a stringy gravity parameter denoted by β.
We show that this parameter is constrained by the shadow existence. Combining
the Newman-Janis algorithm and the Hamilton-Jacobi mechanism, we examine the
shadow behaviors of the rotating solutions in terms of one-dimensional real
curves. Essentially, we find various sizes and shapes depending on the rotating
parameter and the stringy gravity parameter a and β, respectively. To
inspect the shadow geometric deformations, we investigate the astronomical
observables and the energy emission rate. As envisaged, we reveal that a and
β have an impact on such shadow behaviors. For specific values of a, we
remark that the obtained shadow shapes share certain similarities with the ones
of the Kerr black holes in plasma backgrounds. Using the Event Horizon
Telescope observational data, we provide predictions for the stringy gravity
parameter β which could play a relevant role in M-theory
compactifications. We finish this work by a discussion on the behaviors of the
light rays near to such four dimensional black holes by computing the
deflection angle in terms of a required moduli space.Comment: Latex, 27 pages, 10 figures. Authors in alphabetical orde