ASTRO 142 Lecture Notes - Lecture 14: Baryon, Spiral Galaxy, Neutrino
Document Summary
Astro 142: from the big bang to the milky way. The beginning of chapter 15 is in regards to superstructures of the universe - rst the local group galaxy cluster and the local super cluster. The textbook then asks whether the universe has a top-down structure formation (where super clusters fracture into galaxies) or a bottom-up struc- ture (where galaxies coalesce into clusters and super clusters). After the recombination era, the universe entered the dark age" during which no stars existed and no matter had been excited enough to be luminous. During this period, the gases in the universe were neutral but this changed once stars began to form and the radiation from these stars ionized the gas. this re-ionization produced free electrons which could interact with the cbr photons. This provides a method for us to determine the age of the rst stars (determined to be. 200 million years after the big bang).
