Generation Gap In Stars' Orbital Dance
July 19, 2013

Astronomers Track Orbital Motion Of 33,000 Stars In Globular Cluster

[ Watch the Video: Zoom into 47 Tucanae ]

Lee Rannals for - Your Universe Online

Astronomers using NASA's Hubble Space Telescope are tracking the orbital motion of 33,000 stars in one of the Milky Way's oldest globular clusters.

The team will be using the space observatory to track the orbital motion of 33,000 stars within globular cluster 47 Tucanae, which sits over 16,000 light-years away from Earth.

"When analyzing the motions of stars, the longer the time baseline for observations, the more accurately we can measure their motion," says UBC astronomer Harvey Richer, lead author on the paper published in the July issue of Astrophysical Journal Letters. "The Hubble data are so good, we can actually see the individual motions of the stars within the cluster. The data offer detailed evidence to help us understand how various stellar populations formed in such clusters."

The astronomers combined recent Hubble observations with eight years' worth of data from the telescope's archive to determine the motions of the stars in the globular cluster. Our galaxy's globular clusters are the surviving relics from the Milky Way's formation. Scientists say 47 Tucanae is 10.5 billion years old and is one of the brightest of our galaxy's 150 globular clusters. The cluster measures about 120 light-years across and features two populations of stars.

According to the team, the first population of stars consists of redder stars, which are older and less chemically enriched. The second population contains young, blue stars that are more chemically enhanced and move in elliptical orbits.

Past studies revealed many globular clusters contain stars with varying chemical compositions. This suggests multiple episodes for star birth. The latest analysis adds the stars' orbital motion to the mix. The team used Hubble's Advanced Camera for Surveys to look at the cluster in 2010. They combined these observations with archival images to measure the change in position of more than 30,000 stars. This data enabled them to determine how fast the stars move, as well as measure the stars' brightness and temperatures.

Richer and his colleagues are the first team to link stellar dynamics to separate populations. Astronomers will need to continue to analyze these multiple generations better in order to understand how stars formed in distant galaxies in the early universe.