Editing Protogalaxy (section)

===Mechanics===
Once a protogalaxy begins to form, all particles bound by its gravity begin to [[free fall]] towards it. The time taken for this free-fall to conclude can be approximated using the [[Free-fall time#infall to a point source of gravity|free-fall equations]]. Most galaxies have completed this free-fall stage to become stable elliptical or disk galaxies, the disks taking longer to fully form. The formation of galaxy clusters takes much longer and is still in progress now.<ref name="EAAV3" /> This stage is also where galaxies acquire most of their [[angular momentum]]. A protogalaxy acquires this due to gravitational influence from neighbouring dense clumps in the early universe, and the further the gas is away from the centre, the more spin it gets.<ref name=EPiG>{{cite book|last1=Gilmore|first1=Gerard|last2=Wyse|first2=Rosemary F.G.|last3=Kuijken|first3=Konrad|title=Evolutionary Phenomena in Galaxies|date=1989|publisher=[[Cambridge University Press]]|location=Cambridge, UK|isbn=0-521-37193-7|page=194|edition=1st}}</ref>