  Stars and black holes are sources of gravitational radiation in many phases
of their life, and the signals they emit exhibit features that are
characteristic of the generating process. Emitted since the beginning of star
formation, these signals also contribute to create a stochastic background of
gravitational waves. We shall show how the spectral properties of this
background can be estimated in terms of the energy spectrum of each single
event and of the star formation rate history, which is now deducible from
astronomical observations. We shall further discuss the process of scattering
of masses by stars and black holes, showing that, unlike black holes, stars
emit signals that carry a clear signature of the nature of the source.
