Aug 21 2006
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Astronomers reported the first direct evidence of dark matter, an enigmatic substance whose existence scientists had debated. Various theories had suggested that dark matter composes most of the universe’s matter and helps maintain cosmic structures by binding normal matter—such as galaxies’ composite atoms and hot gas—between galaxies. Dark matter is, theoretically, an invisible substance, which scientists can only detect by its gravitational effects on visible matter and radiation. Therefore, scientists had acquired no direct evidence of it until astronomers, led by Douglas Clowe of the University of Arizona, Tucson, discovered such evidence in images that NASA’s HST and other telescopes had captured. The images showed a collision between two galaxy clusters, an event that scientists believed might have been the most energetic event subsequent to the Big Bang. The collision of the clusters had created a wind, causing the formation of a gas cloud with a bullet-like shape. However, the astronomers determined that the gas cloud does not account for most of the matter in the clusters. Instead, a separate, relatively empty patch of space had exerted a gravitational pull on the gas, thereby slowing it down. Because alternative theories of gravity could not account for these results, the astronomers concluded that dark matter had exerted the gravitational pull from the apparently empty area of space.
NASA, “NASA Finds Direct Proof of Dark Matter,” news release 06-297, 21 August 2006, http://www.nasa.gov/home/hqnews/2006/aug/HQ_06297_CHANDRA_Dark_Matter.html (accessed 15 March 2010); Douglas Clowe et al., “A Direct Empirical Proof of the Existence of Dark Matter,” Astrophysical Journal Letters 648, no. 2 (10 September 2006): L109–L113, http://iopscience.iop.org/1538-4357/648/2/L109/ (DOI 10.1086; accessed 29 June 2010).
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