Abstracts of the RTG Colloquium on June 18, 2014

Monica Moscibrodzka
Title: Numerical models of plasma flows onto a supermassive black hole.
Supermassive black holes exist in the centers of many galaxies. Observations
suggest that plasma flows into the deep gravitational potential of black holes, thereby releasing enormous amounts of energy in the form of radiation and powerful plasma outflows, or jets, that can reach way beyond the host galaxy. With radio telescopes, such as the Event Horizon Telescope, we are about to make the first ever images of the event horizon and the plasma flow in the immediate vicinity of black holes. Hence, a theoretical understanding of black hole astrophysics is now crucial and timely.
In particular, numerical simulations give us insight into how these black hole inflows and outflows work and look like.
I will present highlights of general relativistic magnetohydrodynamic simulations of plasma falling onto a black hole. Our models predict dynamical and radiative properties of hot accretion flows around a Kerr black hole. I will show how the observations of the supermassive object in the center of our Milky Way constrain the model parameters. Finally, I will discuss the prospects for detecting the silhouette of the black hole horizon in the center of our Galaxy.

David Hilditch (University Jena)
Free-evolution formulations of General Relativity and their numerical approximation.
Abstract: The choice of coordinates, and the constraints of general relativity give a certain freedom in writing down formulations of the theory. Different formulations may be more or less good from the point of view of the PDEs analyst. I will explain this gauge freedom and what it means for numerical relativity. To illustrate the point I will present simulations of compact binary systems with different formulations.

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