The Physics Factbook™
Edited by Glenn Elert -- Written by his students
An educational, Fair Use website
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|Bibliographic Entry||Result |
|Shipman, Harry L. The Restless Universe: An Introduction to Astronomy. Boston: Houghton Mifflin, 1978: 368.||"Our own Milky Way is a spiral of average mass (200 billion solar masses)."||200 billion |
|Lerner, Rita G. & George L. Trigg. Encyclopedia of Physics. 2nd Edition. New York: VCH, 1991: 736.||"The total mass of the stars and gas in our galaxy is about 200 billion solar masses … its total mass may be 1000 billion solar masses."||200 billion |
|"A Macho Milky Way?" Sky & Telescope. 91, 6 (June 1996): 16.||"Our galaxy contains 490 +/- 110 billion Suns' worth of mass."||380–600 billion |
|Inglis, Stuart J. Planets, Stars, and Galaxies: An Introduction to Astronomy-3rd Edition. New York: Wiley, 1972: 433.||"It is estimated that our galaxy has a mass of 200 billion suns!"||200 billion |
|Imamura, James. Mass of the Milky Way. Astronomy 123. Cosmology.||"The mass contained in the Milky Way (in the visible disk) is 2x1011 M(Sun). [T]he mass contained in the Milky Way galaxy (out to as far as we can see HI gas) is 6x1011 M(Sun)."||200 billion |
As we know, a galaxy is a huge collection of millions, billions,or trillions of stars. The galaxy we live in is called the MilkyWay. The name comes from the literal translation of the Latin"Via Galactica", with via meaning "road"or"way"and the word galaxy from the Greek root "gala",meaning "milk". The Milky Way galaxy is composed ofabout 400 billion stars and is about 100,000 light years in diameter.
The Milky Way is classified as a spiral galaxy and is composedof three main regions:
The total mass of the Milky Way is assumed to be at least 600billion times the mass of the sun, while the densely packed visiblepart is only 200 billion times the mass of the sun. This discrepancyin numbers is believed to be caused by the dark matter in thehalo, since it seems to be taking up mass, but doesn't emit orradiate light. This "missing mass"accounts for almost90% of the mass in the universe. Even though scientists don'tknow what it is, they know it's there because they can detectit by the gravitational effect it has on the surrounding visibleobjects.
Unfortunately, this unknown dark matter is also the determiningfactor in the evolutionary future of the universe. If there istoo little of it to gravitationally bind the the universe together,it can continue expanding forever. If there is enough, though,the universe might slow down the expansion, come to a halt, andbegin to contract and eventually collapse. This is why it is soimportant to find out just what dark matter is and how much ofit there is.
Alina Vayntrub -- 2000
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