2021/12/31 by Leonardo Giani, Oliver F. Piattella, Alexander Yu. Kamenshchik · 11 citations
Physics and Astronomy · #Anisotropy #Ansatz #Astrophysics #Black Holes and Theoretical Physics #Classical mechanics #Cosmology and Gravitation Theories #Equation of state #Friedmann–Lemaître–Robertson–Walker metric #Galaxies: Formation, Evolution, Phenomena #Gravitation #Gravitational collapse #Hydrostatic equilibrium #Isotropy #Mathematical physics #Physics #Quantum mechanics #Spacetime #Universe #astro-ph.CO #gr-qc
paper · pdf · open access · doi:10.1088/1475-7516/2022/03/028
published in Journal of Cosmology and Astroparticle Physics 2022(03), 028 (Institute of Physics) · v2, replaced to match the accepted version. Comments are welcome!
openalex publication_date 2022/03/01 · arxiv created 2022/03/13 · arxiv updated 2022/03/15 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
We investigate a model of gravitational collapse of matter inhomogeneities where the latter are modelled as Bianchi type IX (BIX) spacetimes. We found that this model contains, as limiting cases, both the standard spherical collapse model and the Zeldovich solution for a 1-dimensional perturbation. We study how these models are affected by small anisotropic perturbations within the BIX potential. For the spherical collapse case, we found that the model is equivalent to a closed FLRW Universe filled with matter and two perfect fluids representing the anisotropic contributions. From the linear evolution up to the turnaround, the anisotropies effectively shift the value of the FLRW spatial curvature, because the fluids have effective Equation of State (EoS) parameters w ≈ -1/3. Then we estimate the impact of such anisotropies on the number density of haloes using the Press-Schechter formalism. If a fluid description of the anisotropies is still valid after virialization, the averaged over time EoS parameters are w≈ 1/3. Using this and demanding hydrostatic equilibrium, we find a relation between the mass M, the average radius R and the pressure p of the virialized final structure. When we consider perturbations of the Zeldovich solution, our qualitative analysis suggests that the so called pancakes exhibit oscillatory behavior, as would be expected in the case of a vacuum BIX spacetime.