The Deep Survey - Direct Detection of Dark Matter

As the name suggests, dark matter is dark. It doesn't give off any kind of energy we know about - no light, no x-rays, no microwaves and nothing else. This makes dark matter tricky to study! Astronomers generally use computers to model what dark matter must be like. To compare these models to real life, they look at galaxies or hot gas that are thought to trace the underlying dark matter distribution - but no one is totally sure how well normal matter traces dark matter.

What would be ideal is a way to directly detect dark matter. Gravitational lensing seems to be the most promising way to do it. Gravitational lensing occurs when the light from a distant object is bent - or lensed - by the gravitational field of some massive object along its path. The mass of dark matter will produce "weak lensing" - passing light is bent by just a small amount. The result is that the light from distant galaxies is distorted, until they seem to be stretched out and aligned along the gravitational field of the dark matter.

Because weak lensing by dark matter is such a small effect, astronomers need extremely high quality images of a lot of galaxies to study it. This is where the CFHTLS Deep Survey comes in - it will take exceptionally clear pictures of over two million galaxies. By examining the alignment of these galaxies, astronomers will be able to create maps of the dark matter that's causing the alignments. These plots will be the largest maps of dark matter ever made.