ASTRO 142 Chapter 15: Chapter15ReadingMemo
Document Summary
Galaxies must have formed, perhaps within a billion years after the big bang. Local group: dominated by the milky way and the andromeda. Nearest cluster is the virgo cluster: 18 mpc. Example of an irregular cluster: no particular symmetry and consist mostly of spiral galaxies, with a few elliptical members. Regular clusters: roughly spherical or ellipsoidal in overall shape, and are dominated by elliptical galaxies, with a few spirals. Top-down structure formation: superclusters form first, then fragment into clusters, which shatter into individual galaxies. Bottom-up structure formation: galaxies are fundamental building blocks; galaxies form, then become drawn into clusters by mutual gravitational attraction, followed by the evolution of superclusters as the clusters are pulled together. Hot radiation dominated plasma that emerged from the big bang was remarkably smooth and homogeneous, but contained density fluctuations. This perturbations grew and evolved in complicated ways. Revealed in the pattern of small temperature fluctuations imprinted on the cbr.
