It is known that dark matter interacts gravitationally (and weakly in other ways as predicted by the WIMP model), and dark matter is present in the same space-time fabric as that of matter. When two dark matter ‘objects’ collide then wouldn’t the event produce gravitational waves? And since we know that dark matter is in greater abundance than matter, shouldn’t LIGO and other detectors be detecting,much more frequently, gravitational waves off dark matter collisions than collisions of just observable matter?