The Sagittarius dwarf elliptical galaxy (Sag DEG) is a tiny satellite galaxy orbiting the Milky Way. For aeons, it has been stretched and torn apart by the immense tidal forces of its neighbour. By now, it has been completely absorbed into the Milky Way.
When first discovered, astronomers thought that Sag DEG had already reached an advanced stage of destruction. However, later observations showed that it still had coherence, as a dispersed elongated ellipse. It appeared to be moving in a roughly polar orbit around the Milky Way, reaching as close as 50,000 light years from the galactic core. Computer simulations indicated that stars ripped out from the dwarf would be spread out in a vast "stellar stream" along its path, and these were subsequently confirmed.
Sag DEG may have orbited the Milky Way as many as ten times, prior to being swallowed up. Its ability to retain some coherence, despite such strains, would indicate an unusually high level of dark matter in that galaxy.
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