Two nearby galaxies - long thought to be true companions of the Milky Way - may instead be drifters, passing through the cosmic neighbourhood. Astronomers say the Magellanic Clouds may be moving too fast to be gravitationally bound to our galaxy. If the clouds were satellites of our galaxy, the Milky Way would contain twice as much mass as is thought.
http://news.bbc.co.uk/2/hi/science/nature/6249421.stm