Open AccessA general model of x‐matter
Author(s) -
Aguerri J. A. L.,
Membrado M.
Publication year - 1999
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1999.01975.x
Subject(s) - physics , astrophysics , cosmology , supernova , universe , luminosity , luminosity distance , mathematical physics , dark energy , galaxy
We investigate the cosmology of x‐matter with pressure, p x , and density, ρ x , related by p x =w 0 ρ γ x (w 0 <0;γ >0). For γ >1, this x‐matter behaves like a cosmological constant when a≪ a 0 ( a being the scalefactor and a 0 the scalefactor at present) and like matter for a γ a 0 ; for γ <1, the behaviour is the opposite; for γ =1, the x‐matter density varies as a ‐3 (1+w 0 ). Models of x‐matter with γ >1 reach, at all times, densities lower than do models with γ≤ 1 for equal present x‐matter density, so the former have less effect on the formation of structures in the Universe. Allowed values for the free parameters of these cosmological models are estimated by imposing two observational constraints which originate from the age problem of the Universe and from the luminosity‐‐distance relation for Type Ia supernovae at z =0.4.