The globular star cluster in Abell 1689 is roughly twice as large as any other population found in previous globular cluster surveys -- in comparison, our Milky Way galaxy hosts about 150 -- and constitutes the most distant such systems ever studied, at 2.25 billion light-years away. The Hubble study shows most of the globular clusters in Abell 1689 formed near the center of the galaxy grouping, which contains a deep well of dark matter. The farther away from the galaxy core Hubble looked, the fewer globular clusters it detected. This observation corresponded with a comparable drop in the amount of dark matter, based on previous research.
"The globular clusters are fossils of the earliest star formation in Abell 1689, and our work shows they were very efficient in forming in the denser regions of dark matter near the center of the galaxy cluster," Blakeslee said. "Our findings are consistent with studies of globular clusters in other galaxy clusters, but extend our knowledge to regions of higher dark matter density."
Peering deep inside the heart of Abell 1689, Hubble detected the visible-light glow of 10,000 globular clusters, some as dim as 29th magnitude, which is 1 one-billionth the faintness of the dimmest star that can be seen with the naked eye. Based on that number, Blakeslee's team estimated that more than 160,000 globular clusters are huddled within a diameter of 2.4 million light-years.
"Even though we are looking deep into the cluster, we're only seeing the brightest globular clusters, and only near the center of Abell 1689 where Hubble was pointed," he said.For images and more information about the Abell 1689, visit: http://www.nasa.gov/hubble or http://hubblesite.org/news/2013/36 SOURCE NASA