  We discuss the emission of gravitational radiation produced in encounters of
dark matter galactic halos. To this aim we perform a number of numerical
simulations of typical galaxy mergers, computing the associated gravitational
radiation waveforms as well as the energy released in the processes. Our
simulations yield dimensionless gravitational wave amplitudes of the order of
$10^{-13}$ and gravitational wave frequencies of the order of $10^{-16}$ Hz,
when the galaxies are located at a distance of 10 Mpc. These values are of the
same order as those arising in the gravitational radiation originated by strong
variations of the gravitational field in the early Universe, and therefore,
such gravitational waves cannot be directly observed by ground-based detectors.
We discuss the feasibility of an indirect detection by means of the B-mode
polarization of the Cosmic Microwave Background (CMB) induced by such waves.
Our results show that the gravitational waves from encounters of dark matter
galactic halos leave much too small an imprint on the CMB polarization to be
actually observed with ongoing and future missions.
