Two teams of astronomers have used data from NASA's Chandra X-ray Observatory and other telescopes to map the distribution of dark matter in a galaxy cluster known as Abell 383, which is located about 2.3 billion light years from Earth. Not only were the researchers able to find where the dark matter lies in the two dimensions across the sky, they were also able to determine how the dark matter is distributed along the line of sight.
The team co-led by Tommaso Treu used lensing data from HST and the Japanese telescope Subaru, but added Keck observations to measure the velocities of stars in the galaxy in the center of the cluster, allowing for a direct estimate of the amount of matter there. They found evidence that the amount of dark matter is not peaked as dramatically toward the center as the standard cold dark matter model predicts. Their paper describes this as being the "most robust case yet" made for such a discrepancy with theory. David Sand of Las Cumbres Observatory Global Telescope Network was a member of Treu's team.
The two teams reached contrasting conclusions, most likely stemming from differences in the data sets and the detailed mathematical modeling used. One important difference is that because the Treu et al. team used velocity information in the central galaxy, they were able to estimate the density of dark matter at distances that approached as close as only 6,500 light years from the center of the cluster. The second team did not use velocity data and their density estimates were unable to approach as close to the cluster's center, reaching to within 80,000 light years.