This is the galaxy cluster CL0024+17 and it is located within the constellation Pisces. CL0024+17 is the result of a cataclysmic merger between two large galaxy clusters. As a result, one of the most interesting features of this image deals with the distribution of dark matter.
In the first image, you see the way the galaxy cluster looks after a detailed observation by Hubble. The members of the galaxy group are usually tan in appearance. Behind it, we see the distant galaxies whose light is showing affects of gravitational lensing. By carefully analyzing those background galaxies, scientists are able to map the distribution of the unseen (and largely present) dark matter.
The second image shows the Hubble CL0024+17 observation with a gravity map overlain on top. This allows us to see the concentrations of dark matter, which shows a peculiar ring (instead of simply being a halo). This is likely the remnant of the collision between CL0024+17 and the other galaxy cluster that took place a few billion years ago.