Using n-body and stellar evolution simulations I model different star systems. Through the use of a large number of n-body simulations I model the effect of subvirial initial conditions on the... Show moreUsing n-body and stellar evolution simulations I model different star systems. Through the use of a large number of n-body simulations I model the effect of subvirial initial conditions on the evolution of star clusters and shed light on a dynamical mechanism for rapid mass segregation in young clusters. Using stellar evolution simulations I estimate there to be 10^8 intermediate mass black holes in the local universe. Lastly, I explore the effect of a supernova in a triple star system Show less
The increased availability of accelerator technology in modern supercomputers forces users to redesign their algorithms. These accelerators are specifically designed to offer huge amounts of... Show moreThe increased availability of accelerator technology in modern supercomputers forces users to redesign their algorithms. These accelerators are specifically designed to offer huge amounts of parallel compute power. In this thesis I show how to harness the power of these parallel processors for astrophysical simulations. I start with an introduction that presents the developments in astrophysical algorithms and used hardware since the 1960__s till today. In the following scientific chapters I discuss the use of GPU accelerator technology for direct N-body methods and for the more advanced hierarchical algorithms. These advanced algorithms are more complex to implement on large parallel architectures, but by redesigning the algorithms it is possible to take advantage of the GPU. The developed algorithms are applied to simulate galaxy mergers to explain discrepancies in observational results. In the simulations we test different merger configurations and try to match the results with observational data. The final chapter shows how to scale the developed software code to thousands of GPUs as available in the Titan supercomputer. The in this thesis developed and presented algorithms allow astronomers to take advantage of the new GPU technology and thereby run simulations that contain thousand times more particles than was possible before Show less
The first stars formed a few hundred million years after the Big Bang, when the Universe was only a small fraction of its present age. Their radiation transformed the previously cold and neutral... Show moreThe first stars formed a few hundred million years after the Big Bang, when the Universe was only a small fraction of its present age. Their radiation transformed the previously cold and neutral hydrogen that filled intergalactic space into the hot and ionised cosmic plasma that is observed today. This milestone in the history of the Universe is called the epoch of reionisation. Much about reionisation is still unknown. Computer simulations are one of the most promising theoretical tools to study reionisation. The wealth of high-quality data that will soon be provided by the next generation of telescopes, specifically designed to observe the reionisation event, make it a particularly exciting time to perform such simulations. The thesis "Simulating Cosmic Reionisation" presents TRAPHIC, a novel method to include the transport of ionising radiation emitted by the first stars in simulations of reionisation. TRAPHIC (TRAnsport of PHotons In Cones) is one of the first of a new type of radiative transfer methods that allow the accurate and efficient computation of the growth of ionised regions in representative models of the Universe that contain hundreds of millions of stars. First simulations that employ TRAPHIC on the Dutch national supercomputer Huygens demonstrate the importance of the concepts that underly its design. Show less
