Black Hole And Dark Matter In Modified Gravity

Dark matter problem is an unsolved issue today.On the one hand,dark matter particle is not discovered in terrestrial experiment,the nature of dark matter particle is still a mystery.On the other hand,the evidence for dark matter comes from the gravitational phenomena.Therefore a possible solution to dark matter problem is modifying gravity.Modified gravity theories may not only explain the dark matter,also enrich the content of the study of black hole and can solve some theoretical problems of black hole.In this thesis,a useful theory called Horndeski theory is applied to solve dark matter problem.In the galactic scale,with the help of a black hole solution,an energy density of inverse square law distribution is given so that it can explain galaxy rotation curve.Two-fluid model is used to describe scalar field halo with pressure and give a pressureless dark matter fluid.In cosmological scale,a dark-matter-like behaviour of scalar field fluid can be obtained.Furthermore,we offer a unifying solution for both galactic scale and cosmological scale.