Take the galaxy formation. I've got very little experience with cosmic strings. I barely know what they are. Take the accreting neutron star. 10 -27 is very weak.
Neutron stars are also pretty rare.
Black holes of only a few solar masses probably are, too. Their larger cousins exist usually in the center of galaxies, which are not quite as frequent as stars are. Ah, well, no one said detecting these waves would be easy. I 've mentioned gravitational wave signals and detectors, but I haven't actually described how one would go about detecting gravitational waves. One popular method is to use something called a laser interferometers.