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Speeding to an open universe.

Speeding to an open universe

Careful measurments of the velocity of a group of galaxies seem to indicate that the universe contains insufficient mass to overcome the force of the giant explosion that started its expansion. These data suggest that the universe will never stop expanding, says Gregory D. Bothun of the University of Michigan at Ann Arbor.

Bothun, working with Margaret J. Geller and John P. Huchra of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., determined the velocity of group of galaxies located on the "surface" of a huge bubble embedded in the so-called Great Wall -- a recently identified band and galaxies 500 million light-years long, 200 million light-years wide and 15 million light-years thick (SN: 11/25/89, p. 340). This bubble, whose interior contains very few galaxies, sits next to a significant concentration of galaxies called the Coma cluster.

Bothun's measurments show that the gravitational force exerted by the Coma cluster attracts the galaxies on the bubble surface, pulling them off course from the direction of the universe's expansion. The strength of that attraction depends on how much the rest of the mass in the universe pulls the bubble galaxies away from the cluster. By calculating the Coma contribution, Bothun and his colleagues deduce that the "mean mass density" of the universe is less than one-third that required to reverse its outward expansion.
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Author:Peterson, Ivars
Publication:Science News
Date:Jan 20, 1990
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