page_title: Protogalaxy
section_title: ...to current galaxies
hierarchical_section_title: Protogalaxy / Formation / ...to current galaxies
context_page_description: In physical cosmology, a protogalaxy, which could also be called a "primeval galaxy", is a cloud of gas which is forming into a galaxy. It is believed that the rate of star formation during this period of galactic evolution will determine whether a galaxy is a spiral or elliptical galaxy; a slower star formation tends to produce a spiral galaxy. The smaller clumps of gas in a protogalaxy form into stars.
  The term "protogalaxy" itself is generally accepted to mean "Progenitors of the present day galaxies, in the early stages of formation." However, the "early stages of formation" is not a clearly defined phrase. It could be defined as: "The first major burst of star formation in a progenitor of a present day elliptical galaxy"; "The peak merging epoch of dark halos of the fragments which assemble to produce an average galaxy today"; "A still gaseous body before any star formation has taken place."; or " an over-dense region of dark matter in the very early universe, destined to become gravitationally bound and to collapse."
context_section_description: 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. This follows the process of hierarchical assembly, which is an ongoing process where larger bodies are continually formed from the merging of smaller ones.
caption: An illustration showing protogalaxies colliding
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