NATIONAL HARBOR, Md.—More galaxies are separated by about 490 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 150 megaparsecs, or nearly 490 million light-years, 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 overdense spots could not contain their own pressure, so they emitted sound waves 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–Smithsonian Center for Astrophysics. 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.
These periodic ripples in the spread of galaxies across space are called baryon acoustic oscillations, and they have profound implications for understanding the evolution of the universe. Using such oscillations, astronomers can compare the present-day separation of galaxies with the size of these ripples just after the universe was born to learn how space has stretched over time. “It’s really allowing us to track the expansion history of the universe very accurately,” Eisenstein says. This, in turn, constrains the properties of the dark energy that is driving this accelerating expansion.
via New Cosmic Distance Measurement Points the Way to Elusive Dark Energy – Scientific American.