Null geodesics and shadow of a rotating black hole in extended Chern-Simons modified gravity

LEONARDO AMARILLA; ERNESTO EIROA; GASTON GIRIBET

PHYSICAL REVIEW D - PARTICLE AND FILDS

APS

Año: 2010 vol. 81 p. 124045 - 124045

0556-2821

The Chern-Simons modification to general relativity in four dimensions consists of adding to the Einstein-Hilbert term a scalar field that couples to the first class Pontryagin density. In this theory, which has attracted considerable attention recently, the Schwarzschild metric persists as an exact solution, and this is why this model resists several observational constraints. In contrast, the spinning black hole solution of the theory is not given by the Kerr metric but by a modification of it, so far only known for slow rotation. In this paper, we show that, in the slowly rotating approximation, the null geodesic equation can be integrated, and this allows us to investigate the shadow casted by a black hole. We discuss how, in addition to the angular momentum of the solution, the coupling to the Chern-Simons term deforms the shape of the shadow.