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Among the most striking objects in the universe are glittering, dense swarms of stars known as globular clusters. 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 recent discoveries of young stars in old globular clusters have scrambled this tidy picture.
Instead of having all their stellar progeny at once, globular clusters can somehow bear second or even third sets of thousands of sibling stars. Now a new study led by Chengyuan Li and Richard de Grijs at the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University might explain these puzzling, successive stellar generations. Using observations by the Hubble Space Telescope, the research team has for the first time 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 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.
The KIAA-led research team proposes that globular clusters can sweep up stray gas and dust they encounter while moving about their respective host galaxies. The theory of newborn stars arising in clusters as they "adopt" interstellar gases actually dates back to a 1952 paper. More than a half-century later, this once speculative idea suddenly has key evidence to support it.
Published paper: Li, de Grijs, et al., 2016, Nature, 529, 502–504. "Formation of new stellar populations from gas accreted by massive young star clusters"
Selected press coverage:
The Kavli Foundation:
Interview with Richard de Grijs by the Australian Broadcasting Corporation (ABC news):