The Simplest Picture of Galaxy Formation and Why It Fails
We are now in a position to make a first attempt at understanding how galaxies and the large-scale structure of the Universe came about. In this chapter, we examine the case in which it is assumed that all the matter in the Universe, both ‘visible’ and dark, is in baryonic form. This was the natural starting point for the first plausible models for galaxy formation in the 1960s and 1970s, but they are doomed to failure. Despite this, there are two good reasons for studying this case carefully. The first is that many important physical processes will be introduced which will be needed in the construction of acceptable models. The second aspect is that the failure of these models strongly suggests that the dominant dark matter present in the Universe must be in some non-baryonic form. We need to convince ourselves of the reasoning behind this dramatic conclusion — the nature of the non-baryonic dark matter is of fundamental importance for physics and cosmology.
KeywordsSound Speed Cosmic Background Radiation Galaxy Formation Baryonic Mass Radiation Energy Density
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