Gravitational Lensing

There was a pretty good picture in one of the IfA's friday "coffee-talks" a while ago. This is a picture of a very distant massive cluster of galaxies - many galaxies gravitationally bound to each other. The neat thing was that this cluster acted as a "lens" to warp the image of a galaxy behind it. The somewhat reddish galaxy-like things in the middle are actually twisted and somewhat focused images of a galaxy in the back. Neat. This animation and this Hubble image show the idea a bit better.