Relying solely on a gravitational mirage rather than visible images, astronomers have discovered a previously unknown cluster of galaxies and measured its distance from Earth.
This first-time feat, which uses the properties of mass to infer the location of unseen objects, bodes well for searches of dark matter–the mysterious, invisible material that presumably makes up more than 95 percent of the mass of the universe.
All matter, whether it's visible or not, exerts a gravitational tug. The tug of a massive object not only attracts other bodies but also bends the path of light from more distant objects that lie directly behind it. The bending can elongate the images of distant galaxies, as seen from Earth, or create multiple images of the same object. Th