I proposed a new theory to explain the metallicity gradients observed in elliptical galaxies. This theory is based on the fact that the escape speed is larger in the inner regions of the galaxy. Hence, I proposed the idea that the galactic wind does not arise simultaneously in all the galactic regions. Specifically, it first arises in the outer regions and only later in the inner regions. As a result, the star formation first stops in the outer regions and, consequently, the metallicity is larger in the inner regions. Based on this idea and by using the Instantaneous Recycling Approximation (IRA), I computed the metallicity gradients analytically. Here you can find all the details. Later, in collaboration with Francesca Matteucci, we computed these gradients by relaxing the IRA and by proceeding numerically. Here you can find all the results.