WHAT IS ANATOMY OF THE UNIVERSE ? THE UNIVERSE CONTAINS EVERYTHING that exists ,from the tiniest subatomic particles to galactic super clusters (the largest structures known). Nobody knows how big the universe is ,but astronomers estimate that it contains at least 125 billion galaxies, each comprising an average of 100 billion stars. The most widely accepted theory about the origin of the universe is the Big Bang theory , which states that the universe came into being in a huge explosion the Big Bang that took place between 10 and 20 billion years ago. The Universe initially consisted of a very hot ,dense fireball of expanding, cooling gas. After about one million years the gas began to condense into localized clumps called protogalaxies. During the next five billion years, the protogalaxies continued condensing, forming galaxies in which stars were being born. Today billions of years later, the universe as a whole is still expanding, although th...