Using data from the Sloan Digital Sky Survey, the motion of the satellite galaxies indicated the presence of a much larger, invisible mass. In other words, the larger galaxies are located at the center of giant concentrations of dark matter.
"This is a very important test of our understanding of how the universe works," said one of the researchers, Anatoly Klypin of New Mexico State University. "This is one of the most direct probes of the distribution of dark matter and the properties of dark matter."
The study further found that the gravitational pull of dark matter weakened at its periphery, a unique property not exhibited by bodies composed of ordinary matter.
"We detected a specific law -- the decline in dark-matter density toward the periphery," said Klypin. "The goal of our research is now to measure that law."
Dennis Zaritsky, an astronomer at University of Arizona at Tucson, first postulated dark matter in 1994. Zaritsky saw the excessive motion of satellite galaxies, indicating the presence of an invisible mass, but made no attempt to measure it.
"He was the first to see there was something wrong with motion," said Klypin. "Now (that) weve measured the law, we can reject other theories like MOND."
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