ECAP Seminar: Katarzyna Nowak

Finding evidence for self-enrichment and supermassive stars in forming globular clusters

Self-enrichment is one of the leading explanations for chemical anomalies in globular clusters. In this scenario, a polluter star enriches a forming cluster with its yields, likely ejecting radioactive 26Al into its surroundings. Young massive star clusters, as potential progenitors of globular clusters, provide a valuable setting to investigate self-enrichment processes and assess the role of supermassive stars (>1000 M), which are considered likely polluters contributing to these chemical anomalies.
In the first part of this talk, I will focus on 26Al as a potential tracer of ongoing self-enrichment in young massive star clusters. Detecting 26Al, particularly through its gamma-ray decay lines at 1.8 MeV and 511 keV, as well as 26AlF molecules and positronium radio recombination lines, could provide direct evidence of active self-enrichment. These detections, especially in nearby clusters like R136 in the Large Magellanic Cloud, would offer strong support for self-enrichment scenarios.
The second part of the talk will explore the potential of using 22.2 GHz water kilomasers as tracers of supermassive stars within forming young massive star clusters. Kilomasers, such as the W1 source found in NGC 253, may originate from accretion discs around supermassive stars. Using 2D hydrodynamic simulations, I model the maser spectra for accretion discs around these stars and find that the kilomaser features align well with observed sources like W1, suggesting that kilomasers could indeed signal the presence of supermassive stars.
By examining these two detection methods, I aim to demonstrate how 26Al and kilomasers together provide complementary insights into the processes of self-enrichment and the potential role of supermassive stars in the formation and chemical evolution of globular clusters.