UT: New Clues to the Formation of Globular Clusters

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UT: New Clues to the Formation of Globular Clusters

Post by bystander » Fri May 19, 2023 6:01 pm

New Clues to the Formation of Globular Clusters: Their Ultramassive Stars
Universe Today | Brian Koberlein | 2023 May 16
Globular clusters are odd beasts. They aren’t galaxies, but like galaxies, they are a gravitationally bound collection of stars. They can contain millions of stars densely packed together, and they are old. Really old. They likely formed when the universe was only about 400 million years old. But the details of their origins are still unclear.

We know globular clusters are old because they don’t exhibit any star production, and the stars they contain are old, low-metal stars. This suggests that the clusters formed during the early star-formation period of the universe, and have long since depleted or cast off the dust and gas to form new stars. The stars of a globular cluster have similar ages and chemical compositions, which suggests a globular cluster formed from a single large molecular cloud.

At least that had been the theory. But as astronomers studied globular clusters more closely, they found odd chemical variations within the stars of a particular globular cluster. Some stars have distinct abundances of elements such as oxygen, nitrogen, and sodium not seen in other cluster stars. If the stars of a globular cluster form from the same molecular cloud at roughly the same time, why would some stars be so distinct? A new study ... points to a solution.

In this study, the authors looked at a high redshift globular cluster known as GN-z11. This cluster is at a redshift of z = 10.6, so we see it at a time when it was only tens of millions of years old. Using observations from the James Webb Space Telescope (JWST) they found it a dense cluster of stars active with star production. They also found the cluster had a high relative abundance of nitrogen. This is interesting because such high nitrogen levels are likely produced within early supermassive stars. ...

N-enhancement in GN-z11: First Evidence for Supermassive Stars Nucleosynthesis
in Proto-Globular Clusters-Like Conditions at High Redshift?
~ C. Charbonnel et al
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