Globular star clusters are isolated star cities, home to hundreds of thousands of stars. And like the fast pace of nearly all major cities, these stars are in constant motion, orbiting around the cluster's center. Past observations have shown that the heavyweight stars live in the crowded downtown, or core, and lightweight stars reside in the less populated suburbs.
The heart of the giant globular star cluster 47 Tucanae in this Hubble Space Telescope image reveals the glow of 200,000 stars. In the cluster's crowded core, Hubble spied a population of young white dwarfs starting their slow-paced 40-million-year journey to the quiter, and less dense suburbs.
White dwarfs are the burned-out relics of stars that rapidly lose mass, cool down, and shut off their nuclear furnaces. As these stars age and shed weight, their orbits begin to expand outward from the cluster's packed downtown. This migration is caused by a gravitational tussle among stars in the cluster.
Astronomers use Hubble to analyze all types of stars globular clusters. Also known as NGC 104, 47 Tuc is located 16,700 light-years away in our Milky Way galaxy's southern constellation of Tucana. It is the second brightest globular after Omega Centauri, another southern hemisphere globular. Both are easily visible with the naked eye. Our Milky Way galaxy hosts over 150 of these star cluster cities.
These Hubble observations of 47 Tuc were taken with the Advanced Camera for Surveys and Wide Field Camera 3.
Credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration Acknowledgment: J. Mack (STScI) and G. Piotto (University of Padova, Italy)