Editing Protogalaxy (section)

==Properties==

===Composition===
Since there had been no previous [[star formation]] to create other elements, protogalaxies would have been made up almost entirely of hydrogen and helium. The hydrogen would bond to form H<sub>2</sub> molecules, with some exceptions.<ref name=TSNtDaPG>{{cite journal|last1=Whalen|first1=Daniel|title=The Supernova That Destroyed a Protogalaxy: Prompt Chemical Enrichment and Supermassive Black Hole Growth|display-authors=etal|journal=The Astrophysical Journal|date=16 August 2013|volume=774|issue=1|doi=10.1088/0004-637X/774/1/64|arxiv = 1305.6966 |bibcode = 2013ApJ...774...64W|pages=64|s2cid=59289675}}</ref> This would change as star formation began and produced more elements through the process of [[nuclear fusion]].

===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>

===Luminosity===
The luminosity of protogalaxies comes from two sources. First and foremost is the [[radiation]] from nuclear fusion of Hydrogen into [[helium]] in early stars. This early burst of star formation is thought to have made a protogalaxy's luminosity comparable to a present-day [[starburst galaxy]] or a [[quasar]]. The other is the release of excess [[gravitational binding energy]].<ref name="EAAV3" />
The primary wavelength expected from a protogalaxy is a variety of [[Ultraviolet|UV]] called [[Lyman-alpha]], which is the wavelength emitted by Hydrogen gas when it is [[ionised]] by radiation from a star.<ref name="EAAV3" /><ref name=PGTCDM/>