Speaker
Description
Globular clusters are spheroidal and dense collections of stars with a total mass of up to a few million solar masses that are typically found in the halo of our galaxy and of other galaxies. Their formation dates back to the early Universe and so, they serve as laboratories for understanding the physical processes that chemically enrich and mechanically shape the interstellar medium throughout the history. Observations of globular clusters in the Galaxy show that such clusters frequently host multiple generations of stars being characterized by different age and chemical composition. Thanks to the development of parallelized hydrodynamic simulations, such diversity is now well interpreted in the context of stellar feedback. The powerful winds and radiation from the older stellar content of the cluster is shown to induce thermal instabilities, which lead to accumulation of gas in the interior. Such clumps of gas are self-shielded against the ionizing photons and, when dense enough, they can serve as the primordial material of the posterior stellar generations.
In an effort to capture the dynamical processes that lead to multiple stellar generations within globular clusters, we focused on the properties of five such clusters in the Galaxy. We employed the parallelized three-dimensional FLASH4 hydrodynamic code to simulate the gas dynamic and thermal instabilities. Alongside, we are developing modules that, at each timestep, optimally describe the gas properties, the radiation field, the gravitational forces, and cooling processes of the gas, as well as the formation and dynamics of the clump particles. The ionizing photons, mass, and energy of the stellar winds, collectively regarded as the stellar feedback, were provided by our stellar population synthesis code that is fed with the state-of-the-art models of massive star evolution. Moreover, high energetic sources such as supernovae that occur at the end of the massive star lifetime were further accounted, given that their high mass-loss output via strong ejecta provide significant energy deposit to the medium of the cluster.
Our simulations were run in parallel over ~100 cores per run on the Salomon supercomputer, which is installed on the IT4Innovations National Supercomputing Center. A total of ~700,000 allocated core hours was used for exploring different sets of input parameters and over different resolutions of the computational grid in order to resolve the clumps and capture gas structures. We were able to reproduce the ratio and therefore justify the origin of the diverse generations observed within our studied clusters by means of the in-situ star formation due to dynamical stellar feedback. In addition, we derived an excellent agreement between the stellar mass yield that is inferred by our 3D simulations and the output from our one-dimensional semi-analytical code establishing the latter method as a fast and computationally inexpensive way for quantifying the stellar mass budget.
