Most modern astronomers believe that the universe began about 15 billion years ago when a very dense mass of material exploded in the so-called BIG BANG.  This explosion sent all the materials of the universe outward in all directions, so that our universe is still expanding.  All the galaxies, stars, planets, asteroids and other bodies in the universe were formed or are forming from the gas and dust of this enormous explosion.    New stars continue to be formed, while others die or disappear into “black holes”.