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Dark Matter - Essay

  • Date Submitted: 03/17/2011 11:10 AM
  • Flesch-Kincaid Score: 16.4 
  • Words: 467
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Dark matter
In astronomy and cosmology, dark matter is a conceptualization for observed physical mass at cosmological scales in space where matter itself does not exist. "Dark matter" is inferred to exist based on observed gravitational effects on "visible matter" and background radiation, but is undetectable as matter through emitted or scattered electromagnetic radiation. Its existence was hypothesized to account for discrepancies between measurements of the mass of galaxies, clusters of galaxies and the entire universe made through dynamical and general relativistic means, and measurements based on the mass of the visible "luminous" matter these objects contain: stars and the gas and dust of the interstellar and intergalactic media. According to observations of structures larger than galaxies, as well as Big Bang cosmology interpreted under the "Friedmann equations" and the "FLRW metric", dark matter accounts for 23% of the mass-energy density of the observable universe, while the ordinary matter accounts for only 4.6% (the remainder is attributed to dark energy. From these figures, dark matter constitutes 80% of the matter in the universe, while ordinary matter makes up only 20%.
Dark matter was postulated by Fritz Zwicky in 1934, to account for evidence of "missing mass" in the orbital velocities of galaxies in clusters. Subsequently, other observations have indicated the presence of dark matter in the universe, including the rotational speeds of galaxies, gravitational lensing of background objects by galaxy clusters such as the Bullet Cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies.
Dark matter plays a central role in state-of-the-art modeling of structure formation and galaxy evolution, and has measurable effects on the anisotropies observed in the cosmic microwave background. All these lines of evidence suggest that galaxies, clusters of galaxies, and the universe as a whole contain far more matter than that...


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