This is MACS 1206, a galaxy cluster 4.5 billion light-years from Earth. The photo was taken by NASA's Hubble Space Telescope as part of a new broad sky survey. Can you notice something weird? Yes, some of the galaxies are distorted.
There's no optical error. The galaxies' light is distorted because of dark matter, which bends the light with its gravitational pull. The discovery is quite surprising, as it reveals that previous computer models are wrong. According to these early observations, dark matter is "more densely packed inside [galaxy] clusters" than it was expected.
We will know more about this soon, as astronomers complete this new multi-wavelength survey, called the Cluster Lensing And Supernova survey with Hubble—aka CLASH. The new survey is checking 25 massive galaxy clusters "with unparalleled precision." So far, they have completed six of them. When they are done, we will have a much better understanding of what's going on with dark matter. [NASA]