Formation of the Galaxy
  Current ideas on the formation of the Galaxy are reviewed. Many of the observed characteristics of our Milky Way System are consistent with a scenario in which the Galaxy formed inside out, with the inner part of it evolving by rapid collapse of a single protogalaxy, while the outer halo was accreted over an extended period. A number of possible problems with this "Standard Model" are discussed and summarized in section 5. 
Sidney van den Bergh