LAUSR

We investigate the instability of the unstable circular orbit of a charged null particle to test the strong cosmic censorship conjecture in the near-extremal Reissner-Nordstrom-de Sitter black hole. The instability is estimated as the Lyapunov exponent and found to depend on the mass and charge of the black hole. Then, we explicitly show that the charged null particle in the unstable circular orbits corresponds to the charged massless scalar field in the eikonal limit. This provides a compact relation representing the quasinormal frequency in terms of the characteristics of unstable circular orbits. According to the relation, the strong cosmic censorship conjecture is valid.