These images taken by NASA's Hubble Space Telescope show the globular cluster systems of 100 galaxies observed within the Advanced Camera for Surveys (ACS) Virgo Cluster Survey. Globular clusters, dense bunches of hundreds of thousands of stars, have some of the oldest surviving stars in the universe. Most of the star clusters in the Virgo survey are older than 5 billion years. The Hubble study found evidence that these globular clusters are more likely to form in dense areas where star birth occurs at a rapid rate, instead of uniformly from galaxy to galaxy. Comprised of over 2,000 galaxies and located about 54 million light-years away, the Virgo cluster is the nearest large galaxy cluster to Earth. These composite images were made from the advanced camera's full field-of-view observations. Astronomers also used modeling data to fill in a narrow gap between the camera's detectors. The images were taken from December 2002 to December 2003.