SÉMINAIRE DU GRECO
"Evolution of collisionless, initially cold, self-gravitating systems in one dimension" |
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Stéphane Colombi |
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The matter content of the Universe is, in our "concordance" vision, mainly composed of collisionless "dark" matter interacting only through gravitational force. In that case, the equations of the dynamics to be solved are Vlasov-Poisson equations. But in the highly non linear regime, the resolution of such equations is tricky. For instance, the fine structure of dark matter halos remains a rather mysterious matter when it comes trying to explain why universal profiles such as the so called NFW profile are observed in cosmological N-body simulations, even though there are many tentative but rarely convincing solutions proposed in the literature. Here, presenting the results of an investigation I performed in collaboration with Jihad Touma, I will examine the dynamical properties of an object evolving from cold initial conditions in the one dimensional case, that is in the case where each matter element is an infinite sheet interacting gravitationally with the others. Similarly as in the 3D case, a running power-law density profile builds up, but the structure of the system at its center remains debated, even numerically. Here I shall show results of waterbag, entropy conserving simulations, and try to explain with a simple analytical model what happens at the center of the system. This analytical model is based on a post-collapse Lagrangian perturbative approach iterated at each crossing-time. |
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lundi 8 octobre 2012 - 11:00 Salle des séminaires François Arago, Institut d'Astrophysique de Paris |
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