2004/05/18 by Mustapha Ishak
Physics and Astronomy · #Black Holes and Theoretical Physics #Cosmology and Gravitation Theories #Galaxies: Formation, Evolution, Phenomena #astro-ph #gr-qc
paper · pdf · doi:10.1103/physrevd.69.124027
published as Phys.Rev. D69 (2004) 124027 · 8 pages, 1 figure. To appear in Phys.Rev.D
arxiv created 2004/05/18 · openalex publication_date 2004/06/28 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We use null spherical (observational) coordinates to describe a class of inhomogeneous cosmological models. The proposed cosmological construction is based on the observer past null cone. A known difficulty in using inhomogeneous models is that the null geodesic equation is not integrable in general. Our choice of null coordinates solves the radial ingoing null geodesic by construction. Furthermore, we use an approach where the velocity field is uniquely calculated from the metric rather than put in by hand. Conveniently, this allows us to explore models in a noncomoving frame of reference. In this frame, we find that the velocity field has shear, acceleration, and expansion rate in general. We show that a comoving frame is not compatible with expanding perfect fluid models in the coordinates proposed and dust models are simply not possible. We describe the models in a noncomoving frame. We use the dust models in a noncomoving frame to outline a fitting procedure.