NASA’s Hubble Reveals Link Between Stars' Age and Their Orbits in Dense Cluster

With the help of NASA's Hubble Space Telescope, astronomers have determined the orbital motion of two distinct populations of stars in an ancient globular star cluster, according to a press release.

According to the astronomers, this offers proof that the two distant star populations were formed at different times.

For this study, the researchers led by Harvey Richer of the University of British Columbia in Vancouver, merged the recent observations made by Hubble with eight years of data from the telescopes' archive in order to determine the motion of 30,000 stars in the globular cluster, 47 Tucanae. This is located at a distance of 16,700 light years away in the southern constellation, Tucanae.

For the first time the researchers could link the motion of the stars within the cluster with the stars' age and they found that the two star populations in 47 Tucanae differed 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 within the cluster. The data offer detailed evidence to help us understand how various stellar populations formed in such clusters."

The Milky Way consists of 150 globular clusters and 47 Tucanae is over 10.5 billion years old and is one of the brightest of our galaxy.

The Hubble analysis also supports the previous spectroscopic studies that claim globular clusters have stars of varying chemical compositions indicating several episodes of star birth.

For this, the team used Hubble's Advanced Camera for Surveys to observe the cluster in 2010. They merged those observations with other 754 archival images to measure the changes in position of more than 30,000 stars. With the help of this data the researchers can distinguish the rate at which the stars move. They also measured the brightness and temperature of the stars.

They noticed that the first population had redder stars that were older, less chemically enriched and orbiting in random circles. While the second one had bluer stars that were more chemically enhanced and move in elliptical orbits indicating there were younger stars.

This is the first study to link stellar dynamics to separate populations though prior to this the Hubble has disclosed several generation of stars in globular clusters.