Dark matter

The mysterious force we can't see... and astronomers can’t even agree is there

- Colin Stuart

Our eyes paint such vivid portraits of the world around us that it's easy to forget how much of our surroundings go unseen. WiFi signals pinging this way and that, subatomic particles and radiation zipping about. And, if astronomers are to be believed, there's another invisible interloper to throw into the mix: dark matter.

A cosmic glue thought to help bind the Universe together, dark matter is so prevalent that about a milligram (3.5oz) will pass through your body throughout your life. But where did this notion of 'dark matter' come from?

Its story starts in the 1930s. Astronomer Fritz Zwicky was measuring the speeds of galaxies within a big group called the Coma Cluster. He found many were moving so fast that he would have expected them to break free of the cluster's gravitational shackles and head off on their own. Curiously, they didn't. Zwicky suggested there might be some extra, invisible stuff in the cluster providing an additional gravitational glue. Zwicky called this stuff dunkle materie - dark matter.

Around the same time, the Dutch astronomer Jan Oort was observing stars on the outskirts of our own Milky Way Galaxy. He also found them to be moving faster than expected, meaning they too should be able to break away. But again, they didn't.