47 Tucanae, 16,700 light-years from Earth, is 10.5 billion years old and one of the brightest of our galaxy’s globular clusters.
UBC astronomers have used NASA’s Hubble Space Telescope to track the orbital motion of 33,000 stars in one of the galaxy’s oldest globular clusters, offering new insights into the formation of the Milky Way.
The careful examination of “cosmic choreography” enabled researchers, for the first time, to link the movement of stars within the cluster to the stars’ ages. The study reveals two distinct generations of stars within globular cluster 47 Tucanae, 16,700 light-years from Earth.
The lack of heavier elements in the population of older, redder stars reflects the initial composition of the gas that formed the cluster. After the most massive of these stars completed their stellar evolution, they expelled gas enriched with heavier elements back into the cluster. This gas collided with other gas and formed a second, more chemically enriched generation of bluer stars that was concentrated toward the cluster centre. Over time these stars moved slowly outward into more elliptical orbits.
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.
Astronomers need to continue analyzing these multiple generations to better understand how stars formed in distant galaxies in the early universe.
