Browsing by Author "Oja, Vili"

It is widely believed that most galaxies in our Universe have a supermassive black hole in their center. Black holes play an important role in the evolution of galaxies, and they can offer us a unique way to observe the Universe through gravitational waves. In this Master's thesis I have reviewed the basic properties of black holes and summarized several numerical and computational methods used in simulating the dynamics of black holes at a very high accuracy. One of these methods is the post-Newtonian (PN) expansion, which is a way of approximating the effects of general relativity by adding additional terms to the Newtonian equations of motion, without having to perform challenging full relativistic simulations. I have also simulated two different types of scenarios involving supermassive black holes. First, I have simulated mergers of different black hole binaries to test the effects of the different orders of PN expansion terms on the evolution and lifetime of the system. Secondly, I have simulated stars scattering off of a binary black hole via three-body interactions to probe how these interactions affect the binary and its evolution. Both of these simulated scenarios are important phases during the lifetime of a binary black hole, and interesting to us due to the effects the binary will have on its host galaxy, and the emission of gravitational waves during the merging process. In the PN simulations I studied a binary black hole by varying its initial semimajor axis, eccentricity, and mass ratio. The runs were performed for a total of three times for different PN term configurations. One of the PN simulations produced almost identical results to the analytic formula for the decay of a coalescing black hole binary when only 2.5PN terms were taken into account, showing that the code produces very accurate results to small binary separations. The simulations also clearly showed the highly non-linear nature of general relativity and the PN expansion scheme, as including more terms in the simulation produced results that were hard to predict based on simulations run with lower order terms. The scattering simulations were done to test the effects the stars had on the energy and angular momentum of the binary system. A total of 16 different kinds of system were studied by varying the mass ratio and eccentricity of the black hole binary. The results obtained in this thesis agreed fairly well with similar simulations found in literature. The differences from the literature results can be most likely explained with different initial conditions and the smaller number of runs done in this thesis.