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Scientists open a new chapter of Stellar Parenting

Scientists open a new chapter of Stellar Parenting

Among the most striking objects in the universe are glittering, dense swarms of stars known as globular clusters. Astronomers have for the first time found young populations of stars within these 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. And recent discoveries of young stars in old globular clusters have scrambled this tidy picture.

Now a new study led by researchers at the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University, and including astronomers at Northwestern University, the Adler Planetarium and the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), might explain these puzzling, successive stellar generations.

Globular clusters are spherical, densely packed groups of stars orbiting the outskirts of galaxies. Our home galaxy, the Milky Way, hosts several hundred. Most of these local, massive clusters are quite old, however, so the KIAA-led research team turned their attention to young and intermediate-aged clusters found in two nearby dwarf galaxies, collectively called the Magellanic Clouds.

Brian W. Murphy from Butler University earlier stated that the crowded conditions in globular clusters' cores make it much more likely that stars will physically interact with each other in a variety of ways. It is possible that two stars may collide and form a star with a mass equal to the sum of the masses of its parents. Because these stars are generally more massive than typical stars in the cluster, they will be hotter and bluer, and therefore appear to be younger.

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 study will be published in the Jan. 28 issue of the journal Nature.

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

In a manner of speaking, 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.

Our explanation that secondary stellar populations originate from gas accreted from the clusters' environments is the strongest alternative idea put forward to date, said Richard de Grijs, also an astronomer at KIAA and Chengyuan's Ph.D. advisor. Globular clusters have turned out to be much more complex than we once thought.

What is the most straightforward explanation for these unexpectedly differing stellar ages Some globular clusters might retain enough gas and dust to crank out multiple generations of stars, but this seems unlikely, said study co-author Aaron M. Geller of Northwestern University and the Adler Planetarium in Chicago.

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.

Scientists open a new chapter of Stellar Parenting