DISTANT GALAXIES AND COSMOLOGICAL MODELS
Edward J. Barlow
Member of National Academy of Engineering
Recipient of NASA Public Service Award
Previous member Report Review Committee of the National Research Council
Retired Vice President, Research & Development, Varian Associates
There is evidence of "dynamic dark matter" in halos around galaxies deduced from the pattern of the orbital motions of the stars and gas in these galaxies. Just recently, some of this "dark matter" has been seen faintly in the infrared halo of a nearby galaxy and information is beginning to come in from the X-ray satellite. Some dark matter also exists between galaxies in galaxy clusters. Some of this dark matter might be dead or dying stars. There is even some evidence that neutrinos might have a very small mass and further add to the total, and there may be other forms of dark matter of even more exotic nature called Machos and Wimps, but it is hard to find evidence for more than about 1/3 the critical mass from all known sources.
Our next model, Model IV, shows, in Figure V what the graphs look like for a present age of 15 billion years, a present mass density of 0.3 critical and a negative curvature of space. As would be expected, the results lie between those of Model II and Model III. For one galaxy the curve is developed using numerical integration of the relativistic equations (see Appendix III) and also with a simple analytical expression for the scale factor labeled "best fit". This approximate expression is R(t)~(t 2/3+at) and appears to be quite a close fit. Note that the mass density approaches the critical value as we look further and further back in time toward the big bang. Very soon after the big bang the density would be the critical density to one part in a million or even closer. This is why thinking the mass density must be exactly the critical value has been appealing although experimental data may continue to show a lower mass density.
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