NASA site is announcing that dark matter was discovered by Chandra X-ray Observatory. A teleconference will be held on August 21 at 1 pm EDT (2 pm in Brasil). Sean Carroll is going to participate so the first question is: why wait for one week? Can anyone provide us with more information?
UPDATE: Imagine the collision between two galaxies. The ordinary matter in them collides and gets interlocked due to the mutual gravitational attraction. Dark matter, however, just keeps its momentum and keeps going on leaving behind the colliding galaxies. It seems that something like this has been detected by the Chandra X-Ray Observatory. Collisions of ordinary matter produces a lot of X-rays and the dark matter outside the galaxies acts as a gravitational lens. More details can be found in John Baez.