Protogalaxy (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. Protogalaxies would have been made up almost entirely of hydrogen and helium.
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 initial density perturbation spectrum caused by quantum fluctuations.
This derives from Heisenberg’s uncertainty principle which shows that there can be tiny temporary changes in the amount of energy in empty space 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. This sort of process was reportedly observed and analysed by Nilsson et al. in 2006. 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.
Protogalaxies can theoretically still be seen today, as the light from the farthest reaches of the universe takes a very long time to reach Earth.
There have been many attempts to find protogalaxies with telescopes over the last 30 years because of the value of such a discovery in confirming how galaxies form, but the sheer distance any light would have to travel for it to be old enough to come from a protogalaxy is very large.
This, coupled with the fact that the Lyman-alpha wavelength is quite readily absorbed by dust, made some astronomers think protogalaxies may be too faint to detect.
In 1996, a protogalaxy candidate was discovered by Yee et al. using the CNOC. The object was a disk-like galaxy at high redshift with a very high luminosity. It was later debated that the incredible luminosity was caused by the gravitational lensing of a foreground galactic cluster.
In 2006, K. Nilsson et al. reported finding a “blob” emitting Lyman alpha UV radiation. Analysis concluded that this was a giant cloud of hydrogen gas falling onto a clump of dark matter in the early universe, creating a protogalaxy.
In 2007, Michael Rauch et al. were using the VLT to search for a signal from intergalactic gas, when they spotted dozens of discrete objects emitting large amounts of the Lyman-alpha type UV radiation. They concluded that these 27 objects were examples of protogalaxies from 11 billion years ago.