1 billion years after the Big Bang
After about a billion years, the densest regions of the Universe had become truly massive. Collections of thousands and millions of stars grouped together to form the first galaxies, and then these galaxies collided and merged to form larger galaxies. These regions evolved into the huge super-clusters of Galaxies which we see today.
The way in which the galaxies has grouped together tells us a lot about the contents of the Universe. Primarily, it helps to tell us how much of the Universe is made of “Dark Matter” and “Dark Energy”, which affect the way galaxies interact on the largest scales. Simulations of the Universe run on large super-computers let us compare the virtual Universe with reality. The results of one such simulation, the “Via Lactea” project (Via Lactea is latin for “Milky Way”), are shown below. Only the Dark Matter is shown. At the centre of each bright region of Dark Matter, a galaxy would form, clustering together over time to form a galaxy similar to our own.
After the first generation of stars had exploded, the next generation contained some of the heavier elements present in the Universe at that time. These in turn formed even heavier elements, and when they exploded created some of the heaviest elements we see today, such as uranium and plutonium.
The First Galaxies