That's several questions. I'll try to answer the easier ones first.
It is true that our galaxy has a super-massive black hole (some 3,000,000 solar masses) at its center. I believe that’s fairly typical. Things do fall in and give off energy in the process, as the particles accelerate around on the way in.
I’m not sure what you mean by "en meme temps que la création des particules élémentaires", since the elementary particles did not emerge as a fixed discrete collection of things at some time. Processes of interconversion between particles go on all the time, especially in the hot early moments, with only some special parameters of the collection remaining conserved.
If I understand correctly, the main point of your first question is to ask if there are galaxies beyond the 13.7 billion light-year horizon of what we can see. That depends on what your definition of ’are’ is. Our universe seems to be so homogeneous that, assuming the standard picture in which the homogeneity comes from early inflation is correct, its overall mathematical structure must be at least much bigger than the visible universe. So there should in some sense ’be’ galaxies which will never be visible from Earth, unless there’s some drastic change in the way cosmology is heading.
Could the distant galaxies actually be some sort of wrap-around copies of ones nearby? That wouldn’t happen in standard pictures of cosmology, but a year or two ago it was seriously considered for a while. The motivation was that on the largest scales the cosmic microwave background seems surprisingly homogeneous. One way that could happen would be if we really see the same things in different directions. However, the detailed symptoms expected for a smallish wrap-around universe were not found.
(republished on 07/19/06)