Globular cluster NGC 1783, captured here by the Hubble Space Telescope, is one of the clusters observed by the team. Credit: ESA/Hubble & NASA . Acknowledgement: Judy Schmidt (geckzilla.com)
Recent discoveries of young stars in old globular clusters have upset a long-held theory that globular clusters created all their stars in bulk around the same time.
Astronomers studying this phenomenon have suggested that the discrepancy may be because the clusters are incorporating new, younger stars into the mix from outside, rather than creating them from materials that exist with the cluster.
The results of the study, if true, show how globular clusters can create second or third generations of new stars throughout their lifespan.
Globular clusters are collections of hundreds of thousands, sometimes millions of stars, although the exact nature of their formation and evolution remains unclear.
“This study offers new insight on the problem of multiple stellar populations in star clusters,” says study lead author Chengyuan Li, an astronomer at the Kavli Insititute for Astronomy and Astrophysics at Peking University.
According to the study, globular clusters do not actually incorporate fully formed stars, but rather the external, cosmic material from which they can create new stars themselves.
The study used Hubble observations of globular clusters NGC 1783 and NGC 1696 in the Large Magellanic Cloud, along with NGC 411 in the Small Magellanic Cloud.
“Our explanation that secondary stellar populations originate from gas accreted from the clusters’ environments is the strongest alternative idea put forward to date,” says Richard de Grijs, also an astronomer at KIAA.
“Globular clusters have turned out to be much more complex than we once thought.”
A contrasting theory suggests that new stars are formed from material left behind within that cluster, but co-author of the new study Licai Deng of NAOC believes this is not the case.
“The most massive stars that form in a globular cluster only live about 10 million years before exploding as supernovae, which blow away the remaining gassy, dusty fuel required for making new stars,” he says.
“We have now finally shown that this idea of clusters forming new stars with accreted gas might actually work,” says de Grijs, “and not just for the three clusters we observed for this study, but possibly for a whole slew of them.”
The team now intend to extend their study to other globular clusters in the Magellanic Cloud and the Milky Way.