Abstract <p>This paper shows that when the velocities of particles in a source are small in comparison with the velocity of light any source generates soft gravitational radiation in which the wavelength is much larger then the dimension of the source. In this case only the polarization of gravitons determines the source and it should not depend on its nature: it may be a string, an accelerated electron, or only the gravitational force acting between the particles in the source. The main harmonic is, of course, quadrupole, the rest are small because of the small velocities of the particles in the source. Their observation would be interesting because it would provide information on the particle velocities in the source.</p>