Until now the accepted model of our galaxy has been that there is a supermassive black hole (named Sagitarius A*) in the centre of it. But recently scientists observed an event that really didn't fit into that model.
A gas cloud was passing near the center of our galaxy. According to the black hole model the cloud should have been sucked into the hole. Observations however showed a different result: the cloud passed the center unharmed!
To unravel this disparency between the theory and the observations the scientists had to try out alternative models. Finally, they replaced the black hole with equal mass of dark matter and everything started lining up again.
The new theory is still nowhere near being proved. But it offers an alternate view on our galaxy. In practice, this finding won't have much of an effect. But if it proves to be true it's probably the closest observation of that mysterious dark matter. Of course that still leaves the fact that we still habe no idea what the dark matter itself is.