Abstract

As JWST pushes the limits, astronomers seem to discover galaxies with unusual, extreme, or peculiar properties, which question some of our previous knowledge or potentially even pose more fundamental problems e.g. to our standard cosmological model.

With this background I will present recent results showing evidence for unusual stellar populations (very massive stars, with masses >100 Msun) in different environments/galaxies. I will also discuss possible indications for the presence of supermassive stars (>~1000 Msun) in very compact galaxies and their possible link with globular-cluster formation. Such extreme/unusual stars might be more common in the early Universe and therefore important to understand galaxies, star-formation and possibly also black-hole formation at very high-redshift.