@MISC{Stornaiolo01cosmologicalblack, author = {Cosimo Stornaiolo}, title = {Cosmological Black Holes}, year = {2001} }

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Abstract

In this letter we propose the existence of low density black holes and discuss its compatibility with the cosmological observations. The origin of these black holes can be traced back to the collapse of long wavelength cosmological perturbations during the matter dominated era, when the densities are low enough to neglect any internal and thermal pressure. By introducing a threshold density ˆρ above which pressure and non-gravitational interactions become effective, we find the highest wavelength for the perturbations that can reach an equilibrium state instead of collapsing to a black hole. The low density black holes introduced here, if they exist, can be observed through weak and strong gravitational lensing effects. Finally we observe that we obtained here a cosmological model which is capable to explain in a qualitative way the void formation together with the value Ω = 1. But we remark that it needs to be improved by considering non spherical symmetric black holes. Even if the concept of black hole has been put forward more than 200 years ago[1],it is only in general relativity that a self consistent definition of black holes has been given as a consequence of the Schwarzschild solution. Later the concept of black hole has been extended to arbitrary spacetimes, and it is 1 generally defined as a connected region of a space-like surface from which particles and photons cannot escape to the future null infinity[7]. In the following we shall consider only Schwarzschild black holes, which are defined as bodies of mass M lying completely within a sphere of radius called the Schwarzschild radius[8].