Physics weblogs are all abuzz over a mysterious press release put by NASA entitled NASA Announces Dark Matter Discovery. The main body of the announcement reads:
Astronomers who used NASA’s Chandra X-ray Observatory will host a media teleconference at 1 p.m. EDT Monday, Aug. 21, to announce how dark and normal matter have been forced apart in an extraordinarily energetic collision.
Update. John Baez has been on the case, and he’s deduced the meat of the announcement: a collision of two clusters of galaxies has apparently pulled galaxies and their dark matter halos apart. This provides compelling evidence in favor of the actual existence of dark matter. He has more in the comments, and at his website.