Now we see it: dark matter discovery fills void of knowledge

Australian scientists have helped pin down the position of the mysterious dark matter that makes up 85 per cent of the universe.

Dark matter is invisible, and we do not yet know what most of it is made of. But the latest research shows it is concentrated in the same places as the matter that we are able to see - the galaxies.

An Australian National University astronomer, Matthew Colless, said the discovery demonstrated that, in this regard at least, the universe was less complicated than thought. ``It's always good to find things are simple."

On a grand scale, the galaxies are not spread evenly through space. They are clumped into super-clusters, spread out in big flat sheets, or dotted along long, narrow filaments. The voids between galaxies are vast, hundreds of millions of light years across.

Dark matter could have been spread out more evenly than visible matter, or it could have been much clumpier. Instead, the two are the same.

Dr Colless likened galaxies to campfires atop a mountain range at night. ``You can't see the mountains. But we now know that everywhere you see a fire, it marks the peak of a mountain a concentration of dark matter."

The universe's smallest peaks of dark matter are home to feeble galaxies. ``On top of the Everests you get enormous galaxies."

The finding means the voids really are very empty, containing no visible matter and no dark matter.

British and US researchers used a mathematical model of gravitational attraction to calculate the distribution of dark matter, based on a survey of 210,000 galaxies by Dr Colless's team using the Anglo-Australian Observatory.