And Some Answers Ask your question to the address given below. Later, someone might have noticed some close pairs of galaxies which seemed to be interacting and thought to mention collisions of galaxies. Now we know that the Milky Way is and has been gobbling up neighboring small galaxies, and also that it and most other galaxies had very dramatic early stages, involving massive black holes of up to several billion solar masses. Quasars seem to be massive black holes, active in the early life of galaxies. There are probably billions of white dwarfs, the older versions of stars like our Sun and smaller.
Neutron stars are likewise the endpoints of more massive stars, which are less numerous.
We see a small fraction of them as pulsars. There are probably millions of Neutron Stars. Very rare supermassive stars end up as Black Holes, which are by definition invisible to us. Occasionally we can deduce their presence by their effects on neighboring stars. We know of 9 for sure in the Milky Way and there are doubtless tens or hundreds of thousands.