Black or grey large Boomerang-shaped object flew over mississippi river at night. No lights and completely silent.We were sitting on a roof just east of the Mississippi river stargazing. We then noticed this black object moving in the sky. The object was somewhat difficult to see because it was black with no lights, but it was undoubtedly there. It seemed to be in the shape of a boomerang or plane and it was rather large. Three of us watched as it flew rather slowly and silently north.