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Résumé |
Gravitational collapse is the main mechanism leading to structure formation of different types in the
Universe. The phenomenology depends on the characteristics of the matter involved, with there being a
crucial distinction between zero and non-zero rest-mass particles. In the very early universe, when the
matter is characterised by a barotropic equation of state (pressure proportional to the energy density),
only black holes could have been formed. I the first part of the talk I will explain the mechanism of
formation of these objects, called primordial black holes. They be can be considered as interesting
sources of different signals due to black hole evaporation, as also being the seeds of the very massive
black holes that we think are in the centre of galaxies like the Milky Way. In the second part I will move
to a different problem, analyzing quasi-static spherically symmetric solutions in presence of scalar
fields, to understand the screening mechanism, known as Chameleon. Considering objects such as
standard stars and more compact objects like white dwarfs and neutron stars, I am solving the Tolman-
Oppenheimer-Volkoff equations coupled with the Klein-Gordon equation in a quasi static regime,
keeping into account the background expansion without needing to introduce an artificial cosmic matter
that corresponds to a non-spatially flat metric. The interior of the star is solved using a polytropic
equation of state matching the solution outside onto the cosmic density of an expanding spatially flat
background.
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