  Null cosmic strings are shown to disturb gravitational fields of massive
bodies and create outgoing gravitational waves (GW). Perturbations of the
metric caused by a straight null string and a point-like massive source are
found as solutions to linearized Einstein equations on a flat space-time. An
analytic approximation for their asymptotic at future null infinity is derived.
A space-time created by the source and the string is shown to have
asymptotically polyhomogeneous form. We calculate GW flux in such space-times
and demonstrate that the averaged intensity of the radiation is maximal in the
direction of the string motion. Opportunities to detect null string generated
gravity waves are briefly discussed.
