The innermost stable circular orbit and shadow in the novel 4D Einstein-Gauss-Bonnet gravity
Abstract
Recently, a novel 4D Einstein-Gauss-Bonnet (EGB) gravity was formulated and a spherically symmetric black hole solution in this theory was derived by D. Glavan and C. Lin Glavan:2019inb. In this paper, we study the geodesic motions in the background of the spherically symmetric black hole, by focusing on the innermost stable circular orbits (ISCO) for massive particle and photon sphere and shadow. Also, we find that a negative GB coupling constant is allowable in this theory, as in which case the singular behavior of the black hole can be hidden inside the event horizon. Moreover, we find that due to this extension a recently proposed universal bound on black hole size in Lu:2019zxb can be broken.
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