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Friday, July 19, 2013

Hubble Shows Link between Stars' Ages and Their Orbits in Dense Cluster

Astronomers using NASA's Hubble Space Telescope have for the first time two distinct linked Populations of stars in an ancient globular star cluster to their uniqueness orbital dynamics, offering Proof that the stars do not share the same birth date.


The analysis of the globular cluster 47 Tucanae shows two Populations that Differ in age by less than 100 million years. The cluster reside roughly 16,700 light-years away in the southern constellation Tucana.

Researchers, led by Harvey Richer of the University of British Columbia in Vancouver, recent Hubble observations combined with eight years' worth of data from the telescope's archive to determine the motions of the stars in this cluster.

Previous spectroscopic studies revealed That Contain many globular clusters stars of varying chemical compositions, suggesting multiple episodes of star birth. Hubble This analysis, however it, goes a step further, adding the stars' orbital motion to the analysis.

"When analyzing the motions of stars, the longer the time baseline for observations, the more we can measure accurately Their motion," Richer Explained. "These data are so good; we can actually see for the first time the single motions of the stars in the cluster. The data offer detailed evidence to help us understand how various stellar Populations Such formed in clusters."

The Milky Way's globular clusters are the surviving relics from our galaxy's formation. They offer insights into the early history of our galaxy. 47 Tucanae is 10.5 billion years old and one of the brightest of our galaxy's more than 150 globular clusters. The cluster Measures acerca 120 light-years wide.

Richer and his team used Hubble's Advanced Camera for Surveys in 2010 to observe the cluster. They those observations combined with 754 archival images to accurately measure the changes in positions of more than 30,000 stars. Using these data, they could discern how fast the stars are moving. The team also measured the stellar luminosities as well as temperatures.

This stellar archeology identified the two distinct Populations of stars. The first Consists of redder stars, que are older, less chemically enriched, and in random, circularized orbits. The second population Comprises bluer stars, que are younger, more chemically enhanced, and in more elliptical orbits.

"The redder generation, que is deficient in heavier elements, Reflects the initial motion of the gas That Formed the cluster," Richer said. "These stars have a memory of Their Retained original motion."

After the most massive of these stars completed their stellar evolution, Expelled They gas enriched with heavier elements back into the cluster. This gas collided With Other gas and Formed a second, more chemically enriched generation of stars that was Concentrated towards the cluster center. Slowly over time these stars Have Been moving outwards, putting them on more radial orbits.


This discovery is not the first for Hubble in revealing multiple generations of stars in globular clusters. In 2007 Hubble Researchers found three generations of massive stars in the globular cluster NGC 2808. Richer's team, however I, stellar dynamics linked to separate Populations for the first time. Finding multiple Stellar Populations in Globular clusters have deep cosmological Implications. Astronomers need to solve riddles of these multiple future generations to better understand how stars formed in distant galaxies in the early universe.

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