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Spotlight On .... Dr Raphael Hirschi
Dr Raphael Hirschi is lecturer in Astrophysics. Having gazed at stars in the Swiss countryside throughout his youth, he decided to study physics at the Ecole Polytechnique Federale de Lausanne (EPFL) in order to understand them further. He went on to do a PhD at the Geneva Observatory to study massive stars through theoretical modelling, followed by a post-doctoral position at the University of Basel to investigate the thousands of nuclear reactions taking place in stars and supernova explosions.
In 2007, Dr Hirschi joined Keele as a RCUK Academic Fellow and became a lecturer in 2010. During his time at Keele, he has driven his research on massive stars into two key directions: (1) comprehensive nucleosynthesis in stars and (2) life and death of the most massive stars. (1) Building upon his work on nuclear reactions done in Basel, he has lead a PhD project on the implementation into his stellar evolution code of a comprehensive nuclear reaction network able to follow the complete nucleosynthesis taking place in stars. The inclusion of the comprehensive network was the key development that enabled him and his collaborators to explain unique abundances in the oldest globular cluster of the galactic bulge and thus creating for the first time a link between the galactic bulge and metal poor stars, results published in Nature. (2) Following the link between SN2007bi and pair-creation supernova, he directed another PhD project on the computation of the first grid of rotating massive stars models above the commonly accepted upper mass limit of 150 solar masses. These models enabled Dr Hirschi and colleagues to "weigh" the most massive stars known to date that his collaborators later discovered in the R136 cluster. The most massive star discovered, R136a, has a birth mass of 320 solar masses, thus challenging our understanding of "how massive can stars be?".
More recently, he has initiated new research directions: comprehensive nuclear sensitivity studies with Prof Rauscher (Basel) and combining 3-dimensional (3D) and 1D simulations of rotation-induced mixing in collaboration with Prof Roepke (Wuerzburg, D) in order to improve the modelling of stellar rotation. In 2008, he was appointed visiting scientist at the World Premier Institute of the Physics and Mathematics of the Universe in Japan and is the first UK associate partner of the European Eurocore programme, Eurogenesis.
This year, Dr Hirschi secured a prestigious grant from the European Research Council (ERC); the first awarded to a Keele Academic. The ERC starting grant will fund a 5-year multi-disciplinary project entitled SHYNE (Stellar HYdrodynamics, Nucleosynthesis and Evolution), which started on November 1 2012. The grant will enable Dr Hirschi to build a team of two post-doctoral researchers and two PhD students, all based at Keele, and to acquire a dedicated computer cluster comprising 1000+ CPU cores. The computer cluster, supplied by Integrex HPC (UK), will have 288 cores virtually sharing memory through the innovative hardware developed by the Norwegian company Numascale. The SHYNE team will collaborate with Numascale in order to determine the best balance between shared and distributed memory architectures, adding an inter-sectoral component to the project.
The SHYNE project will develop an innovative software suite that draws upon numerical techniques from several disciplines, with the goal of extending them in their application to produce state of the art theoretical models of stars. This software suite will produce comprehensive datasets of stellar evolution models that will provide a theoretical framework of analysis for astronomical observing facilities (ESO VLT, E-ELT & ESA GAIA). This project will also use stellar models as a virtual nuclear physics laboratory to guide and boost the return on investments in large nuclear physics experiments (e.g. FAIR at GSI, D).
This project will tackle many challenging questions and unsolved problems: How are the elements we are made of created? What are the properties of the most massive stars and what is their fate? Do electron-capture supernovae exist? What are the most important nuclear reaction rates and what precision in nuclear physics experiments is desirable for astrophysics applications? How does one improve 1-dimensional models using modern computers and multi-dimensional simulations? What is the best computer platform for medium- and large-scale simulations? The SHYNE project will thus have a wide ranging impact on the various disciplines involved, build a promising bridge with a high-tech company and boost Dr Hirschi's research.
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