Gravitational lensing effects of black hole with conformally coupled scalar hair

Abstract

Abstract In this paper, we investigate the gravitational lensing effects in the weak and strong field limits of a static black hole with conformally coupled scalar field. In the weak field limit, with the use of Gauss–Bonnet theorem we calculate the deflection angle of the light. It is found that comparing to Schwarzschild and Reissner–Nordstr $$\ddot{\text {o}}$$ o ¨ m (RN) black holes in general relativity, the weak deflection angle can be enhanced/suppressed by the scalar hair. In the strong field limit, we first compute the light deflection angle via calculating the lensing coefficients, all of which increase as the values of electric and scalar charges increase. Then we evaluate the lensing observables in strong field regime by supposing the hairy black hole as the candidate of M87* and SgrA* supermassive black holes, respectively. We find that the scalar hair has significant influences on various observables. In particular, the lensing observables of the charged black hole with positive scalar hair and RN black hole have degeneracy, which will be broken by the case with negative scalar hair. Our theoretical findings imply that it is feasible to employ the gravitational lensing effects as a probe of Einstein–Maxwell theory with negative scalar field differentiating from general relativity, once the future astrophysical observation is precise enough.