The Cartwheel Galaxy, a spectacular interacting galaxy, in a picture by the Hubble Space Telescope. In ancient times, it was a spiral, its strange current shape having been produced when a small galaxy on the right traversed it centrally. This false colour image shows blue areas which indicate zones of energetic star-forming activity, while the yellow present in the nucleus and inner ring is due to interstellar dust. Between the inner and outer rings, there are fragments that could be remnants of the old spiral arms or the embryos of newly forming arms.