Link between stars’ ages and their orbits




These images showcase the ancient globular cluster 47 Tucanae, a dense swarm of up to a million stars. The entire cluster (left) was taken by the U.K. Schmidt Telescope Oct. 12, 1977 and Sept. 9, 1989. NASA’s Hubble Space Telescope image in rectangular box was taken between January and October 2010
Image Credit: NASA, ESA, DSS,STScI/AURA/UKSTU/AAO,Univ. of Br. Columbia

The analysis enabled researchers, for the first time, to link the movement of stars in the clusters with the stars’ ages. The two populations in 47 Tucanae differ in age by less than 100 million years.

“When analyzing the motions of stars, the longer the time baseline for observations, the more accurately we can measure their motion,” said Richer. “These data are so good, we can actually see the individual motions of the stars in the cluster. The data offer detailed evidence to help us understand how various stellar populations formed in such clusters.”


Previous spectroscopic studies revealed many globular clusters contain stars of varying chemical compositions, suggesting multiple episodes of star birth. This Hubble analysis supports those studies, but adds the stars’ orbital motion to the analysis.

Richer and his team used Hubble’s Advanced Camera for Surveys to observe the cluster in 2010. They combined those observations with 754 archival images to measure the change in position of more than 30,000 stars. Using these data, they could discern how fast the stars move. The team also measured the stars’ brightness and temperatures.



This is not the first time Hubble has revealed multiple generations of stars in globular clusters. In 2007, Hubble researchers found three generations of stars in the massive globular cluster NGC 2808. But Richer’s team is the first to link stellar dynamics to separate populations.
