SDSS luminous red galaxies concentrations

The best gravitational lenses for detecting distant galaxies are those with the largest mass concentrations and the most advantageous configurations of that mass along the line...

用于探测遥远星系的最佳引力透镜（gravitational lenses），是那些具备最大质量集中度，且其质量沿视线方向排布最为有利的天体系统。