Study reveals why giant star clusters could be home to variously aged star populations

A team of Chinese and U.S. researchers has found evidence to explain why globular clusters can somehow bear second or even third sets of thousands of sibling stars, instead of having all their stellar progeny at once, according to a study published online Wednesday in the journal Nature.

Globular clusters are spherical, densely packed groups of stars orbiting the outskirts of galaxies. Astronomers had long thought globular clusters formed their millions of stars in bulk at around the same time, with each cluster's stars having very similar ages, much like twin brothers and sisters. Yet the recent discoveries of young stars within old globular clusters have scrambled this tidy picture.

Using observations by the Hubble Space Telescope, the team, led by researchers at the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University, focused their attention on young and intermediate-aged clusters found in two nearby dwarf galaxies, collectively called the Magellanic Clouds.

The team found young populations of stars within globular clusters that have apparently developed courtesy of star-forming gas flowing in from outside of the clusters themselves.

This developing method stands in contrast to the conventional idea of the clusters' initial stars shedding gas as they age in order to spark future rounds of star birth, according to the study.

"Our study suggests the gaseous fuel for these new stellar populations has an origin that is external to the cluster, rather than internal," said study lead author Chengyuan Li, an astronomer at the KIAA.

The discovery "offers new insight on the problem of multiple stellar populations in star clusters," said Li. That means globular clusters appear capable of "adopting" baby stars - or at least the material with which to form new stars - rather than creating more "biological" children as parents in a human family might choose to do.

The team thus proposes that globular clusters can sweep up stray gas and dust they encounter while moving about their respective host galaxies.

"We have now finally shown that this idea of clusters forming new stars with accreted gas might actually work," said Richard de Grijs, co-author of the study.

Future studies will aim to extend the findings to other Magellanic Cloud as well as Milky Way globular clusters, according to the team. Endit