We propose a single-phase super lens with a low density that can achieve focusing of sound beyond the diffraction limit. The super lens has a star-shaped lattice structure made of steel that offers abundant resonances to produce abnormal dispersive effects as determined by negative parameter indices. Our analysis of the metamaterial band structure suggests that these star-shaped metamaterials have double-negative index properties, that can mediate these effects for sound in water. Simulations verify the effective focusing of sound by a single-phase solid lens with a spatial resolution of approximately 0.39 lambda. This superlens has a simple structure, low density and solid nature, which makes it more practical for application in water-based environments.