Editing Protogalaxy (section)

==Formation==

It is thought that the early universe began with a nearly uniform distribution (each particle an equal distance from the next) of matter and dark matter. The dark matter then began to clump together under [[gravitational attraction]] due to the [[Structure formation#Cosmological perturbations|initial density perturbation spectrum]] caused by [[quantum fluctuation]]s.<ref name="EAAV3" /> This derives from [[uncertainty principle|Heisenberg's uncertainty principle]] which shows that there can be tiny temporary changes in the amount of energy in empty space.{{citation needed|date=May 2019}} Particle/[[antiparticle]] pairs can form from this energy through [[mass–energy equivalence]], and gravitational pull causes other nearby particles to move towards it, disturbing the even distribution and creating a centre of gravity, pulling nearby particles closer. When this happens at the universe's present size it is negligible, but the state of these tiny fluctuations as the universe began expanding from a single point left an impression which scaled up as the universe expanded, resulting in large areas of increased density. The gravity of these denser clumps of dark matter then caused nearby matter to start falling into the denser region.<ref name=HotU>{{cite book|last1=Seagrave|first1=Wyken|title=History of the Universe|date=2012|publisher=Penny Press|url=http://historyoftheuniverse.com/index.php?p=firstStars.htm|access-date=18 July 2014|archive-url=https://web.archive.org/web/20140728163133/http://historyoftheuniverse.com/index.php?p=firstStars.htm|archive-date=28 July 2014|url-status=dead}}</ref> This sort of process was reportedly observed and analysed by Nilsson et al. in 2006.<ref name=CAoDMH>{{cite journal|last1=Nilsson|first1=K.K.|display-authors=etal|title=A Lyman-α blob in the GOODS South field: evidence for cold accretion onto a dark matter halo|journal=Astronomy and Astrophysics|date=June 2006|volume=452|issue=3|pages=L23–L26|doi=10.1051/0004-6361:200600025|arxiv = astro-ph/0512396 |bibcode = 2006A&A...452L..23N |s2cid=14837456}}</ref><ref name=RBU>{{cite web|title=Rare Blob Unveiled: Evidence For Hydrogen Gas Falling Onto A Dark Matter Clump?|url=https://www.sciencedaily.com/releases/2006/07/060703163148.htm|website=ScienceDaily.com|access-date=22 July 2014}}</ref> This resulted in the formation of clouds of gas, predominantly [[hydrogen]], and the first stars began to form within these clouds. These clouds of gas and early stars, many times smaller than our galaxy, were the first protogalaxies.<ref name=PGTCDM>{{cite web|last1=Johnston|first1=Hamish|title=Proto-galaxies tip cold dark matter|url=http://physicsworld.com/cws/article/news/2007/nov/28/proto-galaxies-tip-cold-dark-matter|website=Physicsworld.com|access-date=18 July 2014|date=2007-11-28}}</ref>

[[File:Stellar Fireworks Finale.jpg|thumbnail|An illustration showing protogalaxies colliding]]
The established theory is that the groups of small protogalaxies were attracted together by gravity and collided, which resulted in the formation of the much larger "adult" galaxies we have today.<ref name=PGTCDM/> This follows the process of hierarchical assembly, which is an ongoing process where larger bodies are continually formed from the merging of smaller ones.<ref name=EAAV3/><ref>{{cite book|last1=Freeman|first1=K|last2=Larson|first2=R.C|last3=Tinsley|first3=B|title=Galaxies: Sixth Advanced Course of the Swiss Society of Astronomy and Astrophysics|date=1976|publisher=[[Geneva Observatory]]|location=Sauverny, Switzerland|pages=75–82}}</ref>