This week, astrophysicists has announced the first prove that
As far as I understand it, a collison of two galaxy clusters was observed with an X-Ray telescope, and the existence of Dark Matter was proven by mapping the gravitational fields. This wouldn’t be so significant if not for the fact that in this collison, the visible matter was removed from the Dark Matter. The non-interacting Dark Matter went right through the collision and the normal matter was at a different place, so they could deduce that Dark Matter was present. The other possibility that was always present in observations when this seperation didn’t occur was that the gravitational force would just need a modification. In this case, a modification of gravitation isn’t able to explain the observed gravtational fields.
Here’s an article by Sean Carroll on CosmicVariance about it, and for those who don’t like reading, there’s an audio segment on Science Friday where Sean talks as a guest. He also shortly talks about the much more mysterious Dark Energy.