NASA's Hubble Space Telescope has found the largest known population of globular star clusters, about 160,000, inside the core of the giant grouping of galaxies known as Abell 1689.
An international team of astronomers used Hubble's Advanced Camera for Surveys to discover this bounty of stellar fossils and confirm such compact groupings can be used as reliable tracers for dark matter, the invisible gravitational scaffolding on which galaxies are built.
Lead author Karla Alamo-Martinez of the Center for Radio Astronomy and Astrophysics of the National Autonomous University of Mexico in Morelia, said that they show how the relationship between globular clusters and dark matter depends on the distance from the center of the galaxy grouping.
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.
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.
The study has been published in The Astrophysical Journal.