Evolution

The luminosity of the astrophysical objects depends depends partly on the medium in which it evolves/moves. In particular, their chemical composition evolves/moves in the course of time and in a different way according to the galaxies. This evolution could have significant consequences on the physics of the studied objects and could modify their intrinsic luminosity in the course of time.

This type of evolution has in theory a significant influence on the spectra of the objects. The variations of metalicity entered of the modifications of spectrum. Moreover, one does not know at the present time mechanisms allowing to modify the intrinsic luminosity of an object without modifying his spectrum of it.