Elliptical galaxies are classified by their shape . Basically, this means that E0 elliptical galaxies appear precisely circular , while E7 galaxies are long and skinny , with E1, E2, etc, denoting the range of shapes in between. Spiral Galaxies . Unlike elliptical galaxies, spiral galaxies contain a disk component . They also contain gas, dust, hot bright stars and areas of star formation .
Globular clusters are also present, so they contain both old and young stars.
Normal spirals this type of spiral galaxy has a round or elliptical bulge in the center, and spiral arms . Sa these have large nuclear bulges and tightly wound arms. They have little gas and dust. Barred spirals this type of spiral galaxy is similar to a normal spiral, except that there is a bar in the middle , and the arms come out of the bar. SBb intermediate SBc small nuclear bulge and bar, and loosely wound arms.