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More galaxies are separated by 450 million light-years than by any other large distance, astronomers have found in the most precise measurement yet of this key cosmic length scale. Using this scale, researchers calculated astronomical distances with a record low level of 1 percent uncertainty in a measurement that helps clarify what is behind the unexplained dark energy causing the universe's expansion to accelerate.

The separation of 450 million light-years, or 150 megaparsecs, is an artifact of the birth of the universe, which created tiny ripples in the density of matter that caused material in some spots to clump together into the seeds of galaxies. When the universe was young and very hot, these over-dense spots could not contain their own pressure, so they emitted sound waves out into space that traveled until the universe cooled down and neutral atoms formed. "Basically every one of these regions in the universe has thrown off a sound wave which has traveled off for a distance that is 150 megaparsecs today," says Daniel Eisenstein of Harvard University. And where those sound waves stopped, they gave the matter there a kick that made it, too, more likely to form the seed of a galaxy. Eisenstein, who directed the Sloan Digital Sky Survey (SDSS) III that collected the data used for the measurement, presented the results today here at the 223rd meeting of the American Astronomical Society.

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