Nonradial stability of marginal stable circular orbits in stationary axisymmetric spacetimes

Understand

We study linear nonradial perturbations and stability of a marginal stable circular orbit (MSCO) such as the innermost stable circular orbit (ISCO) of a test particle in stationary axisymmetric spacetimes which possess a reflection symmetry with respect to the equatorial plane.

• The proposed approach is applied to Kerr solution and Majumdar-Papapetrou solution to Einstein equation.
• Finally, we reexamine MSCOs for a modified metric of a rapidly spinning black hole that has been recently proposed by Johannsen and Psaltis [PRD, 83, 124015 (2011)].
• We show that, for the Johannsen and Psaltis's model, circular orbits that are stable against radial perturbations for some parameter region become unstable against vertical perturbations.