Radiation-reaction-induced evolution of circular orbits of particles around Kerr black holes

It is demonstrated that, in the adiabatic approximation, nonequatorial circular orbits of particles in the Kerr metric (i.e., orbits of constant Boyer-Lindquist radius) remain circular under the influence of gravitational radiation reaction. A brief discussion is given of conditions for breakdown of adiabaticity and of whether slightly noncircular orbits are stable against the growth of eccentricity. © 1996 The American Physical Society.