Elliptical galaxies

Elliptical galaxies have a spherical or oval shape with no internal structure and approximately uniform brightness. The stars within them come and go in all directions in a haphazard way. If they were not moving, they would eventually fall towards the center of the galaxy and it would collapse under its own gravity, but because of their movement, the stars are subjected to a centrifugal force that prevents them from fall towards the center.

The elliptical galaxies are mainly composed of old and red stars and are more or less devoid of young and massive stars. They contain only a very small amount of gas and dust and the interstellar medium is virtually non-existent. These two facts are related since gas is the necessary ingredient for star formation. If it is absent, no new star can be formed and all the stars present were formed at a time when interstellar gas was still available. These are necessarily stars with a very long life, so not massive and red