Globular clusters, which are glittering and dense swarms of stars in the universe, were long considered by astronomers as the ones having formed their millions of stars in bulk around the same time. And thus, it was thought as if each cluster's stars had very similar age. But this notion has been decried by recent discoveries of young stars in old globular clusters.

Researchers, in a new study published in the January 28 issue of the journal Nature, have claimed that instead of bearing all their stars at once, globular clusters can have second or even third sets of thousands of sibling stars.

The study was led by researchers at the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University and it included astronomers at Northwestern University, the Adler Planetarium and the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC).

The research team used observations by the Hubble Space Telescope and has for the first time found populations of young stars within globular clusters that probably may have developed due to star-forming gas flowing in from outside the clusters. Earlier, it was believed that initial stars in clusters shed gas to spark the future rounds of star birth.

“This study offers new insight on the problem of multiple stellar populations in star clusters”, said study lead author Chengyuan Li, an astronomer at KIAA and NAOC.

Li, who is also affiliated with the Chinese Academy of Sciences' Purple Mountain Observatory, said the study suggests the gaseous fuel for these new stellar populations has an origin that is external to the cluster rather than internal.

Another astronomer at KIAA, Richard de Grijs, said their explanation that secondary stellar populations originate from gas accreted from the clusters' environments was the strongest alternative idea put forward to date.