Gravitational Radiation from a Particle Scattered by a Kerr Black Hole

Abstract

We have computed the energy, linear and angular momentum of the gravitational radiation emitted by a particle of mass µ scattered by a Kerr black hole of mass M(≫µ) and angular momentum 0.99M2G/c (i.e., a=0.99M G/c).The particle is at rest at infinity and its orbital plane is perpendicular to the spin axis of the black hole. It is found that contrary to the Schwarzshild case quasi-normal modes of the black hole can be excited by the particle which corotates with the spin axis of the black hole and has sufficiently small orbital angular momentum. In this case, the gravitational radiation carries the large amount of linear momentum of order of 10−1(µ/M)µc, while for counterrotating cases order of 10−3(µ/M)µc. For the same absolute value of the orbital angular momentum a counterrotating particle emits more energy than a corotating one, because the angular velocity at the periastron of the former is greater than that of the latter. A scattered particle excites the quasi-normal mode under the condition that twice the angular velicity at the periastron is greater than the real part of the frequency of the quasi-normal mode.