ASTRO 142 Chapter Notes - Chapter 15: Massive Compact Halo Object, Galaxy Merger, Baryon
Document Summary
Structure forms because of the gravitational attraction of the matter content of the universe. Most of this matter is nonluminous dark matter: the nature of this unseen dark matter is one of the most important outstanding cosmological problems. Galaxies, including the milky way, appear to be surrounded by huge spheroidal dark halos of unknown composition observations have indicated that some of the halo mass must take the form of compact objects called machos. At larger scales in the universe, clusters are found to represent great accumulations of dark matter. We conclude that some 90% of the matter in the universe is not only invisible, but nonbaryonic. It consists of some type of weakly interacting massive particle, since anything that interacted more strongly would have significant observational and physical consequences. One obvious candidate of for such a wimp is the neutrino. The origins of the structure lie within the earliest moments of the big bang.
