Most of the space in the universe is empty. Part of the reason for the emptiness of space is that the matter in the universe is
gravitationally attracted to other pieces of matter. Most matter in the universe gets pulled into one of the many massive systems held together by the gravitational pull of black holes. These massive systems can be millions of light years wide and contain millions of stars and planets. What do scientists call these massive systems?
Galaxies? (I think that is the answer if it’s not sorry) but Anwyays I’ll explain it is called galaxy because each of our galaxies have our own solar system, their own sun, planets and all living things.
