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Cosmology
The Formation and Evolution of Galaxies
One of the greatest and possibly most important questions about our universe is how it originated. Astronomer Sandy Faber of California's Lick Observatory states that, "Galaxies are the building blocks of the universe, and therefore one of the greatest questions of modern astronomy is to understand how they form." (Chaikin)
Galaxy is usually understood as a cluster or aggregate of stars - combined gas and dust - held together by gravity. Galaxies come in three main types: ellipticals, spirals, and irregulars. (The Galaxies) There are a number of theories about the formation of galaxies. Two predominant theories are the Bottom-Up and Top-Down theories. The Bottom-Up theory states that the Universe started from small particles of mass that came together to form galaxies, which evolved into clusters and then super-clusters. (ibid) The second theory - the Top-Down theory - states that "vast pancaked-shaped clouds of matter...
There is controversy about which came first - black holes or galaxies and clusters. While some scientists are of the opinion that black holes appeared at the centre of existing star groups, others think that the black holes formed first and drew stars around them.
Black holes are "objects with a gravitational field so strong that its escape velocity exceeds the speed of light. In other words, a black hole is an object whose mass and size are such that…
Bibliography
Britt R. Astronomers Capture Images of Quasar from When the Universe was Young. Space.com. January 9, 2003. Accessed:
http://www.space.com/scienceastronomy/distant_quasar_030109.html
Chaikin. 5 Great Cosmic Mysteries: The Origin of Galaxies. Space Com. January 22, 2002. Accessed: April 30, 2004. www.space.com/scienceastronomy/astronomy/cosmic_galaxies_020122-1.html
New class of black holes. Nature. September 19, 2002. Accessed: May 1, 2004. http://www.nature.com/nsu/020916/020916-9.html
The Galaxies. Accessed: 2 April, 2004. http://sankofa.loc.edu/savur/web/THEGALAXIES.html
Wikipedia: Black holes. Accessed: May 1, 2004. http://en.wikipedia.org/wiki/Black_holes
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