i've heard it said that the power of the mind can be multiplied one hundredfold

I am neither a scientist or astronomer but as my mind is hundred times better than most I can only assume that you need to point yourself at me!!! Only joking, I have never heard that before. Perhaps it is for the same reasons that the positions of the planets are thought to influence temperament and personality, because of the magnetic pull influencing the electrical current and liquid content of our bodies. I can see the logic in that with the moon for example as it is so close. With the centre of the universe thing, I think that an astronomer would need to find the edges before they could say where the centre was and they are nowhere near doing that. I would guess though that you probably don't need to know where it is to do that exercise. The power of it would lie in your belief and the quality of your visualisation rather than exact coordinates. No one needs a photo of God to get something from prayer (fortunately) and the same applies here. In fact, I would be willing to bet that a large part of the beneficial effect of this would come from the focusing itself which would act as a form of meditation and this would give you all the well-documented benefits that meditation produces. Focusing on any point would probably work just as well but saying that you need to focus on a bit of space somewhere on the northern edge of the galaxy and a bit to the left doesn't have the same ring to it. Sorry just noticed that it said galaxy not universe - an astronomer probably would know that but my answer still stands. If you wanted an image in your mind though you could probably get some pretty good pictures of the centre of the galaxy on space sites. I know that we are in one of the outside arms.