Research on gravitational waves based on black hole perturbation theory

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In recent years, much attention has been paid to establishing the basis for gravitational wave astronomy, that is, to understand physics of gravitational wave sources accurately.In this project, adopting the black hole perturbation approach, we focused on the orbital evolution of a binary system with a supermassive black hole and a compact star that includes gravitational radiation force. In this approach, a compact star is approximated as a point. particle and this requires us to regularize the reaction force acting on it. To derive the regularized reaction force, it is necessary to solve a so-called gauge problem as well as to construct an accurate and efficient method of regularization.To solve the gauge problem, we proposed two methods: One is to regularize the reaction force in the harmonic gauge and the other is to do so in the Regge-Wheeler gauge. Through this research, we made clear how the gauge problem can be solved.As for constructing an efficient method of regularization, we developed an analytical method based on the post-Newton expansion. The advantage of this method is, though it needs the post-Newton expansion, once the calculation is done it can be applied to any orbit.At present, we are investigating the necessary post-Newton order for an actual computation of the orbital evolution, and it will be made clear in the near future.