Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aas...18312504c&link_type=abstract
American Astronomical Society, 183rd AAS Meeting, #125.04; Bulletin of the American Astronomical Society, Vol. 25, p.1477
Astronomy and Astrophysics
Astronomy
Scientific paper
X-ray observations of hot gas are ideal for measuring the total gravitating mass and the hot gas mass of a spherical system provided the gas is in hydrostatic equilibrium and has well-defined temperature and density profiles. These conditions are satisfied for Abell 1991, a richness class 1 cluster with a central cD galaxy at z = 0.0589. ROSAT PSPC observations reveal that the system is well-modeled with a hydrostatic beta model where beta = 0.55. The temperature has a minimum in the central region, increases with radius and then decreases at large radii; the mean emission-weighted mean cluster temperature is 1.3 keV. The ratio of the gaseous to total gravitating mass is 0.2-0.25 within a radius of 0.5 Mpc. If this baryonic fraction is representative of the mean value in the universe, it is impossible to accommodate an Omega =1 universe simultaneously with Big Bang nucleosynthesis.
Bregman Joel N.
Cox Caroline V.
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