Visible to the naked eye, the Large and Small Magellanic Clouds are two of the Milky Way's closest companion galaxies. Scientists have assumed that these groups of stars have been orbiting the Milky Way for billions of years. But new measurements of the speed of these familiar fixtures now put astronomers in unfamiliar territory. Either the two tiny galaxies are just whizzing by or our galaxy is twice as massive as many scientists had estimated.
To record the motion of the clouds of stars as they inch across the sky, Nitya Kallivayalil of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and her colleagues used the Hubble Space Telescope. This velocity is notori