Matter warps the space around it. The more matter there is, the stronger the warp. For really strong distortions of space-time, like black holes, the warping acts like a lens. Such gravitational lenses have been found, and astronomers can use them to study very distant and very faint galaxies.
“Hubble’s Universe” is a recurring broadcast from HubbleSite, online home of the Hubble Space Telescope. Astrophysicist Frank Summers takes viewers on an in-depth tour of the latest Hubble discoveries. Find more episodes at HubbleSite.org.
Astronomers Find One of the Youngest and Brightest Galaxies in the Early Universe
http://hubblesite.org/newscenter/archive/releases/2008/08/