20-05-2024  11:00
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Alvio Renzini - INAF Osservatorio di Padova

Globular clusters are among the oldest objects we know of, many likely to have formed at the epoch of reionization, and may have even contributed to it. Their formation, with their ubiquitous multiple stellar generations, remains an intriguing puzzle in astrophysics. Direct evidence indicates that they formed in a series of bursts, and each burst did not prevent the occurrence of the following ones, as if there was no negative feedback on star formation. Moreover, second-generation stars exhibit different light-element abundances, but no sign of enhancement by supernova products which, together with the lack of feedback, indicates that formation took place before supernovae started to affect the ISM.
This suggests that, above a critical mass, stars fail to produce supernova events, but rather sink into black holes without ejecting much energy and heavy metals. This scenario of globular cluster formation has the attractive implication of suppressing star formation feedback for some ~10 million years, in practice leading to runaway star formation, analog to overcooling that in the absence of feedback would have turned most baryons into stars in the early Universe. Under such conditions, multiple episodes of star formation, incorporating stellar ejecta from previous bursts, appear to be unavoidable, thus accounting for the ubiquity of the multiple-generation phenomenon in globular clusters. If this is indeed the way globular clusters formed, then a generic ~10 Myr delayed feedback
would have important implications for star formation in general, and in particular for the very high redshift Universe, helping to account for the unexpected frequency of bright/massive galaxies at z=9-16 revealed by JWST.

Globular cluster formation and the high-redshift Universe
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