Modern cosmology and the dark matter problem by Sciama, Dennis William

By Sciama, Dennis William

This ebook indicates how sleek cosmology and astronomy have ended in the necessity to introduce darkish topic within the universe to account for mass. a few of this darkish subject is within the time-honored kind of protons, electrons and neutrons, yet such a lot of it should have a extra unique shape. the popular, yet now not the one, chance is neutrinos of non-zero relaxation mass, pair-created within the sizzling great bang and surviving to the current day. After a overview of contemporary cosmology, this publication provides an in depth account of the author's fresh idea during which those neutrinos decay into photons which are the most ionizing brokers in hydrogen and nitrogen within the interstellar and intergalactic medium. This thought, even though speculative, explains a couple of quite assorted confusing phenomena in astronomy and cosmology in a unified approach and predicts values of varied vital amounts equivalent to the mass of the decaying neutrino and the Hubble consistent

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The arc would then appear at this position. Since the core radius of the visible matter in A370 is observed to exceed 0 a (~ 25") it follows that the dark matter in this cluster is more concentrated than the visible. 16 Dark Matter in Clusters of Galaxies A further point made by Bergmann et al. is that if @p > Qa the total mass of the cluster would be improbably large. These results have been confirmed by Guhathakurta (1992) who studied 26 clusters and found that all the optically rich and/or compact ones show appreciable lensing.

This has dimensions £~~2, so to obtain a dimensionless quantity we multiply by R2/'R2{— H~2). 2 Models of the Universe 27 We thus take as our definition of the deceleration parameter q the equation RR This is a purely kinematical definition. If we adopt the dynamical laws (5) and (6) and use (4) we find a- 4X °P (9) which shows the way in which q measures the density of matter p. In general q changes with time but an interesting exception is the Einstein-de Sitter model (k = 0) in which R oc t*, and so q = \ at all times.

In order to 12 Dark Matter in Clusters of Galaxies demonstrate this they computed from the mass model a quantity 7, defined as the ratio between the mass in diffuse dark matter and the mass in gas and in galaxies (inclusive of their dark haloes) at two different radii. 8 X 1014 M 0 and the mass associated with galaxies (assuming with Hughes and Tanaka that M/Ly — 5) is 4 x 1013 M 0 . 2 Mpc. 2 Mpc. However, they considered that a more realistic value of M/Ly would be 20. They then found that 7 goes from ~ 1 to ~ 10 over the same radial interval.

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