To see any distance in space, you need some kind of telescope. We’ve got some pretty powerful ones here on Earth, but nature has us beat with gravitational lenses. This is a phenomenon when a relatively nearby object passes directly between us and a more distant object. The gravity from the nearby object acts like a telescope lens to bend light and magnify the more distant object. Until now, these gravitational lenses have been single stars or distant galaxies, but now a new class of lenses is being called into service: entire groups of galaxies! The research is being done as part of the Canada-France-Hawaii Legacy Survey which will devote 500 nights of telescope time over the next 5 years.

R. A. Cabanac et al.: The CFHTLS strong lensing legacy survey (PDF)