May 18 2004
From The Space Library
A group of astronomers reported new findings concerning two prominent enigmas of physics ~ dark energy and the expansion of the universe. Steve Allen of Cambridge University led a group of scientists who had used NASA's Chandra X-ray Observatory to examine 26 clusters of galaxies, located 1 to 8 billion light-years from Earth ~ a span of time covering the universe's initial explosion and subsequent expansion. Previously, many scientists had theorized that a force called dark energy might have counteracted gravity, causing the expansion. Chandra's observations of the distances between the galaxy clusters indicated that the universe's expansion had accelerated, and Chandra's data on the ratio of hot gas to dark matter within the galaxy clusters indicated that the density of dark energy had not changed. Both findings were contrary to many previous hypotheses. The astronomers stated that, although their findings were inconclusive, the data suggested that the constant density of dark energy causes the universe to expand eternally. This finding is consistent with Albert Einstein's concept of cosmological constant, which states that the universe expands constantly and gradually. (NASA, “Chandra Opens New Line of Investigation on Dark Energy,” news release 04-163, 18 May 2004; Guy Gugliotta, “Astronomers Find More Evidence of 'Dark Energy',” Washington Post, 19 May 2004.
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