Galaxy clusters: The missing mass in stars

In galaxy clusters, the iron mass contained in the gas seems proportional to the virial mass. We proposed that this virial mass is made of stars and/or star remnants which produced the iron in the past. Here we examine the dynamical behaviour of clusters in which the bulk of the missing mass is made of such objects. We show that the relaxation due to distant encounters between galaxies and these background objects permit to explain the observed relationships between the central galaxy densities and both the total optical luminosities and the galaxy mean velocities.