default header
16 May 2006
International Astronomers Publish Largest 3-D Map of Universe
Map to help show how matter is distributed in universe
Washington – A team of astronomers has published the largest three-dimensional (3-D) map of the universe ever constructed, a wedge-shaped slice of the cosmos that spans a tenth of the northern sky and extends 5.6 billion light-years deep into space.
Leading the team was Nikhil Padmanabhan of the U.S. Department of Energy (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab) and David Schlegel of Princeton University, according to a May 15 Berkeley Lab press release.
They and their international coauthors are members of the Sloan Digital Sky Survey (SDSS), an effort that is managed by the Astrophysical Research Consortium for the 25 international participating institutions.
SDSS funding is provided in part by the participating institutions, DOE, NASA, the U.S. National Science Foundation, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England.
"What's new about this map is that it's the largest ever," says Padmanabhan, "and it doesn't depend on individual spectra" – meaning the intensity of electromagnetic radiation (such as ultraviolet, visible light and infrared) across a range of wavelengths.
The principal reason for creating large-scale 3-D maps is to understand how matter is distributed in the universe, Padmanabhan said.
“Because this map covers much larger distances than previous maps,” Schlegel said, “it allows us to measure structures as big as a billion light-years across."
The distribution of galaxies reveals many things, but one of the most important is a measure of the mysterious dark energy that accounts for some three-fourths of the universe's density.
Dark matter accounts for roughly another 20 percent, while less than 5 percent is ordinary matter of the kind that makes visible galaxies.
"Dark energy is just the term we use for our observation that the expansion of the universe is accelerating," Padmanabhan said.
"By looking at where density variations were at the time of the cosmic microwave background" – about 300,000 years after the Big Bang – "and seeing how they evolve into a map that covers the last 5.6 billion years,” he added, “we can see if our estimates of dark energy are correct."
Cosmic microwave background radiation is a form of electromagnetic radiation discovered in 1965.
Most cosmologists consider this radiation the best evidence for the Big Bang model of the universe – that the universe emerged from a hugely dense and hot state about 13.7 billion years ago.
The new map shows that the large-scale structures are distributed in keeping with current ideas about the accelerating expansion of the universe.
The map's assumed distribution of dark matter, which although invisible is affected by gravity just like ordinary matter, also conforms to current understanding.
The SDSS 2.5-meter telescope at Apache Point, New Mexico, was used to create the new map of the universe.
Text of the press release is available at the Berkeley Lab Web site, and the Sloan Digital Sky Survey is available online.
(Distributed by the Bureau of International Information Programs, U.S. Department of State. Web site: http://usinfo.state.gov)
