Globular star clusters, dense bunches of hundreds of thousands of stars, contain some of the oldest surviving stars in the Universe. A new international study of globular clusters outside our Milky Way Galaxy has found evidence that these hardy pioneers are more likely to form in dense areas, where star birth occurs at a rapid rate, instead of uniformly from galaxy to galaxy.
Astronomers used the NASA/ESA Hubble Space Telescope to identify over 11 000 globular clusters in the Virgo cluster of galaxies, most of which are more than 5 billion years old. Comprised of over 2 000 galaxies, the Virgo cluster is located about 54 million light-years away and is the nearest large galaxy cluster to Earth. Along with Virgo, the sharp vision of Hubble's Advanced Camera for Surveys (ACS) resolved the star clusters in 100 galaxies of various sizes, shapes, and brightness – even in faint, dwarf galaxies.