Protogalaxy
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 (normal) 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
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
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.[5] This follows the process of hierarchical assembly, which is an ongoing process where larger bodies are continually formed from the merging of smaller ones.[1][6]
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 H2 molecules, with some exceptions.[7] 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 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.[1] 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.[8]
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.[1] The primary wavelength expected from a protogalaxy is a variety of
Detection
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, in some places long enough that we see them at the stage where they are populated by protogalaxies. 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.[9]
In 1996, a protogalaxy candidate was discovered by Yee et al. using the Canadian Network for Observational Cosmology (CNOC). The object was a disk-like galaxy at high
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.[3][4]
In 2007, Michael Rauch et al.[12] 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.[5]
See also
References
- ^ ISBN 978-0-333-75088-9.
- ^ Seagrave, Wyken (2012). History of the Universe. Penny Press. Archived from the original on 28 July 2014. Retrieved 18 July 2014.
- ^ S2CID 14837456.
- ^ a b "Rare Blob Unveiled: Evidence For Hydrogen Gas Falling Onto A Dark Matter Clump?". ScienceDaily.com. Retrieved 22 July 2014.
- ^ a b c d Johnston, Hamish (2007-11-28). "Proto-galaxies tip cold dark matter". Physicsworld.com. Retrieved 18 July 2014.
- ^ Freeman, K; Larson, R.C; Tinsley, B (1976). Galaxies: Sixth Advanced Course of the Swiss Society of Astronomy and Astrophysics. Sauverny, Switzerland: Geneva Observatory. pp. 75–82.
- S2CID 59289675.
- ISBN 0-521-37193-7.
- ^ Bothun, Gregory D. "Protogalaxies". Caltech.edu. Retrieved 18 July 2014.
- S2CID 1421568.
- S2CID 14392384.
- S2CID 16974679.