A team of astronomers using the Hubble Space Telescope were able to resolve an accretion disk in a quasar. Quasars are active galactic nuclei, consisting of a black hole in the center of a galaxy accreting matter and spewing out radiation as it does so.
The technique they used involved the effects of gravitational lensing. From relativity, we know that any amount of mass bends the space-time in its vicinity. This causes other masses, and light, to follow curved paths in three dimensional space. If there is a large amount of mass in the path of light between another object and us, it will cause the light to bend around it, effectively creating a lens. Stars in the way of our view to the distant quasar observed allowed learning a great number of details about its accretion disk. Particularly, the accretion disk is between four and eleven light-days across. The accretion disk can be seen in the above picture as the faint shape around the two bright areas. These two areas are the images of the quasar formed by gravitational lensing.
As I wrote previously, quasars are difficult objects to observe, and now observations like this one are starting to catch up with theory.
Image Credit: NASA, ESA, and J.A. Muñoz (University of Valencia)