Dark matter is postulated to exist in order to explain the gravitational force which holds galaxies together. There is not enough visible matter to explain it.
Members of the international Dark Energy Survey (DES) team – a collaborative effort to reveal the nature of the mysterious dark energy that is driving the expansion of our universe – have created a map that covers a quarter of the sky of the southern hemisphere (an eighth of the total night sky visible from Earth).
The team used an international supercomputer to analyse images of 100 million galaxies, looking at their shape to see if the light had been stretched. This is one way to investigate dark matter.
If the light from distant galaxies has been distorted, it suggests there is matter in the way, bending the light as it comes towards us. Astronomers are mapping these distortions which may suggest invisible, but gravitating, mass.