Abstract: Star clusters are dense and old groups of stars held together by self-gravitation, typically orbiting around (larger and less dense) galaxies. They are actually amongst the densest and oldest astrophysical structures of the Universe. Formed more than 10 billion years ago, they have witnessed and survived all the steps along the evolution of the galaxies around which they orbit. Therefore, they constitute unique probes of the history of the Universe, and in particular of our home galaxy, the Milky Way. Yet, the improvement of the observational techniques and ressources of the last decade has revealed that decoding the story told by clusters is more challenging than previously thought. Numerical simulations to the rescue! This problem is however notoriously complex, being the poster-child example of a multi-physics and multi-scale topic: up to 13 orders of magnitudes in time and spatial scales must be captured by simulations to reach a predictive nature. This multi-scale bottleneck can be, somehow seamlessly, overcome with increased computational power. But the multi-physics aspect, where complex hydrodynamics must be solved jointly with star-by-star gravitation is the real challenge. To date, no numerical technique allows to model jointly the formation and evolution of a star cluster together with its host galaxy, which hinders theoretical progress in this field. In this talk, after an introduction of the problem and the state of the art, I will present our curent efforts to add a collisional treatment in the Boltzmann equation to solve the star-by-star dynamics within the dense star clusters, while maintaining a much faster collision-less and hydrodynamical description for the rest of the galaxy. I will illustrate how our new method paves the way to a new generation of astrophysical simulations, by tackling long-lasting questions in the field.
About the speaker: Florent Renaud is a CNRS researcher in the GALHECOS team at Strasbourg Observatory since October 2023. After completing his PhD between Vienna and Strasbourg back in 2010, he moved to CEA-Saclay, Surrey (UK) and Lund (Sweden) for various post-doctoral appointments. He then became staff in Lund from 2019 to 2023. He recently obtained a fellowship from the Institute for Advanced Studies of the University of Strasbourg (USIAS) in 2023 and was concomitantly hired as a Research Director of the CNRS at Strasbourg Observatory. His research focuses on the formation and evolution of galaxies, their internal structure and their interstellar medium, with the aim to better understand the complete cosmic baryon cycle.
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