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Défense publique de thèse de doctorat en mathématiques

Par François Staelens : "Cosmological Spherical Collapse with Relativistic Hydrodynamics and Threshold for Primordial Black Hole Formation".

Catégorie : défense de thèse
Date : 20/11/2020 16:00 - 20/11/2020 19:00
Orateur(s) : François STAELENS
Organisateur(s) : André FÜZFA


  • Alexandre MAUROY (UNamur), président
  • André FÜZFA (UNamur), promoteur et secrétaire
  • Christophe RINGEVAL (UCLouvain)
  • Sébastien CLESSE (UNamur et UCLouvain)
  • Eric GOURGOULHON (Observatoire de Paris)


This work is devoted to the study of the gravitational spherical collapse of pressured matter in a cosmological background using the tools of numerical relativity. The thesis is divided into two parts.

In the first one, we investigate the universality of the critical collapse with respect to the matter type by considering the constant equation of state ϖ as a control parameter. It is shown numerically, in the cases the background is Minkowski or de Sitter, that the mass of the formed black hole, for sub-critical solutions, rescales in a power-law of |ϖ-ϖ*|, where ϖ* is the critical ϖ, with an exponent independent of the matter type. For the full matter Friedmann-Lemaître-Robertson-Walker background, serious indications in favour of universality are exposed but some numerical noise from the Einstein-de Sitter outer boundary conditions prevents us to prove it completely.

The second part investigates the hypothesis that Dark Matter is made of Primordial Black Holes (PBH) by computing the critical delta at several moments of the postinflationary thermal history of universe, when the equation of state knows some dips that favour their formation. The peaks in the PBH mass function of [Carr et al. 2019b] are shown to be attenuated and shifted towards lower masses. These results seem to reject the initial hypothesis but the importance of the gauge choice is pointed out.


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