This false color visible light image shows two galaxies that have collided and are merging. The brighter parts of the galaxies are shown in red, the fainter parts in green. The merger is still in process, and the resulting new galaxy has a very irregular shape (see the comparative optical view).
Neutral hydrogen gas, mapped by its 21 centimeter emission, is shown in blue. Notice that neutral hydrogen is found only in the ΓÇ£tails,ΓÇ¥ which were drawn out during the collision. While spiral galaxies contain a great deal of neutral hydrogen gas, elliptical galaxies do not. This image suggests this is because neutral hydrogen is expelled during the collisions out of which elliptical galaxies may form.
