What the Universe is made of
The Universe looks the same in whichever direction you look and from wherever you look at it. This means that we are not in a special place in the Universe.
The Sun is one of lots of stars in a big collection called a galaxy. Our galaxy is called the Milky Way. The Milky Way is one of many galaxies in a group called a cluster. Clusters also come in groups called superclusters, which are dotted around the Universe with gigantic gaps in between them.
In 1929, an astronomer called Edwin Hubble found that all of the galaxies in the Universe are moving away from each other. This is because the whole Universe is getting bigger.
The way that some galaxies move makes us think that there is more stuff in the Universe than we can see. We call this missing stuff “dark matter”.
Scientists think that there are two types of dark matter – hot and cold. Hot dark matter is made up of particles called “neutrinos” that are very light and move very fast.
Cold dark matter is moving much more slowly but is also much heavier. We don’t know what makes up cold dark matter, but it is probably either particles called “axions” and “photinos”, or very small black holes. So far no-one has been able to find any of these, but scientists are still looking.
Click on the links below to find out more about the Universe.
Authors: Carolyn Brinkworth and Claire Thomas
Last updated: July 2001