TIDAL DISRUPTION OF THE MAGELLANIC CLOUDS BY THE MILKY-WAY

Interactions between galaxies are common, and influence physical prope rties such as the global morphology and star-formation rate(1) (Hubble type). Galaxies can interact in many different ways: they can merge t ogether; they can pass through each other, with gas being stripped fro m the smaller of the two and compressed in the larger; and they can in teract gravitationally(2) (including, for example, tides in clusters). The relative importance of these mechanisms is often not clear, as th e strength of each depends on poorly known parameters such as the dens ity, extent and nature of the dark-matter haloes that surround galaxie s(3). A nearby example of a galaxy interaction where the mechanism is controversial is that between our Galaxy and two of its neighbours, th e Magellanic Clouds. Here we present the results of an atomic-hydrogen survey that help to elucidate this mechanism. Our data reveal a new s tream of gas that lies in the opposite direction to the trailing Magel lanic Stream and leads the motion of the Clouds. The existence of both leading and trailing streams supports a gravitational interaction whe reby the streams are torn from the bodies of the Magellanic Clouds by tidal forces.