Clouds of Magellan

In recent years astronomers have found a number of surprises in the structure of the Magellanic clouds themselves. Tides raised by their interaction with each other and with the Milky Way have distorted their form, and there is now a long tendril of gas and stars extending between the LMC and the SMC. One reconstruction of the history of the clouds suggests they collided or at least had a near-miss some 200 million years ago. The author and his colleagues have proposed that the SMC was torn apart by such an encounter and now consists of two misshapen galaxies superposed along the authors line of sight. Perhaps the most remarkable of the recent discoveries is the Magellanic Stream, a plume of hydrogen gas that trails behind the clouds, extending over more than a quarter of the sky. The stream may indicate a violent future for the Magellanic clouds: they could be destined to fall into the core of the Milky Way. The clues to these events, both past and future, lie in the relations between the two clouds and in their interaction with the Milky Way. The Magellanic clouds are often described as dwarf companions of the Milky Way, as if they were analogous to the moons of a planet. Actually it is not certain that the clouds are gravitationally bound satellites of our galaxy. Furthermore, the clouds are not dwarfs; they are galaxies of medium size and are small only in comparison with the Milky Way, which is a quite large spiral galaxy. 7 figures