Astronomers Map Distribution of Dark Matter in Abell 383

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. Abell 383 is located about 2.3 billion light years from Earth. Researchers also able to determine how the dark matter is distributed along the line of sight. The recent work on Abell 383 provides one of the most detailed 3-D pictures yet taken of dark matter in a galaxy cluster. The X-ray data (purple) from Chandra in the composite image show the hot gas, which is by far the dominant type of normal matter in the cluster. Galaxies are shown with the optical data from the Hubble Space Telescope (HST), the Very Large Telescope, and the Sloan Digital Sky Survey, colored in blue and white. Both teams combined the X-ray observations of the normal matter in the cluster with gravitational lensing information determined from optical data. The team of Andrea Morandi from Tel Aviv University in Israel and Marceau Limousin from Universite de Provence in France and University of Copenhagen in Denmark concluded that the increased concentration of the dark matter toward the center of the cluster is in agreement with most theoretical simulations. Their lensing data came from HST images. The team led by Andrew Newman of the California Institute of Technology and Tommaso Treu of University of California, Santa Barbara (UCSB) 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. The contrasting conclusions reached by the two teams most likely stem from differences in the data sets and the detailed mathematical modeling used. One important difference is that because the Newman’s 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. Morandi and Limousin 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. Another important difference is that Morandi and Limousin used a more detailed model for the    3-D map of dark matter in the cluster.