What determines the shape of elliptical galaxies?
There is very little structure visible in elliptical galaxies, unlike the magnificent forms we see in the spirals. Elliptical galaxies are simply vast collections of stars that remain relatively close together because of the gravitational attraction between them. Unlike the spirals there is no well defined rotation axis, so the stars in the galaxy show a wide range of orbital paths around the centre. The motions of stars are not entirely random, however. There is a degree of uniformity in the direction of these motions, and this determines the overall shape of the galaxy. The system of classifying the ellipticity of these galaxies can produce labels up to E10, but in reality we only see objects of classes up to and including E7.
