Large Scale Structure of the Universe

Galaxies are not scattered at random throughout the Universe. They are arranged in a definite pattern (which we will see in the next few pages). It is believed that dark matter helped to form this large-scale structure during history. This, it seems, was the invisible hand which gathered the gas of the young Universe into stars and galaxies.

We have seen that the Cosmic Microwave Background Radiation is not perfectly smooth. It is filled with the tiny variations in the density which had been left over from the inflaton field when it was blown up during inflation. These tiny variations became the large-scale variations in the density we see in the CMBR.

It is believed that the dark matter in the young Universe was also denser in some places than others. Over time, gravity contracted these dense regions so they became denser still, the sites where stars and galaxies formed.

By using the theory of dark matter and computers to simulate history, astronomers have been able to re-create how the present structure might have developed. Let us look at some of these simulated pictures.