THE ELLIPTICAL GALAXIES

The elliptical galaxies have the shape of a more or less flattened ellipsoid. They are named with the letter E, followed by a number from 0 to 7, indicating the lower or higher flattening (the E0 galaxies are the most spheroidal, the E7 ones the most flattened). The galaxies of this kind are less bright than the spiral ones with equal mass, therefore they seem less numerous, but they probably are less than half of the total.
The elliptical ones are the galaxies with the larger variety of mass and size: there are the dwarf elliptical ones, with masses only a few million times larger than that of the Sun, and diameters measuring 5,000 light years, and then there are the giant ones, with a mass 10,000 billion times that of the Sun and diameters 300,000 light years long. The latter are situated especially in the centre of the clusters of galaxies.
The elliptical galaxies have hardly any gas and young stars (like the massive ones, of the 0 and B spectral type). Instead, the old stars are prevalent; these are cold, and therefore they belong to the last spectral types: the spectrum of these galaxies is red. All the stars originated in the early phases of the life of these galaxies, using up almost all the available gas; the rest was expelled by the galaxy, after its heating up caused by violent processes, such as the explosions of supernovae.
The elliptical galaxies are a lot more homogenous than the spiral ones, both in terms of stellar content and distribution of the stars.
Mosaic of pictures of the NGC 4881 galaxy (centre of the image). This is an elliptical galaxy that belongs to the Coma cluster, a large cluster of galaxies, five times farther than the Virgo cluster. (HST) 

 
 
The M105 galaxy, of the E1 type, in the Leo constellation. (N.R. Tanvir)

 
 
The EO M89 galaxy, in the Virgo constellation. (SEDS)

 
 
The galaxy type E2 M60. It is situated in the Virgo constellation. (SEDS)