Penn State scientists help construct largest 3-D map of the universe

August 08, 2012

UNIVERSITY PARK, Pa. -- The Sloan Digital Sky Survey III (SDSS-III), an international collaboration that includes Penn State astronomers, has produced the largest-ever three-dimensional map of massive galaxies and distant black holes. The new map will help to explain the mysterious "dark matter" and "dark energy" that scientists know makes up 96 percent of the universe.

The map is the first in a series planned during a six-year project that will fully expand into three dimensions the largest-ever 2-D image of the sky, which the SDSS-III released early last year. The scientists constructed the new 3-D map from the project's first two years of data, which it published recently as "Data Release 9" (DR9), making it freely available to astronomers, students, teachers and the public. A high-resolution image and an animation can be found at online.

"This data release considerably expands upon the work of the first two phases of the SDSS," said Donald Schneider, distinguished professor and head of the Department of Astronomy and Astrophysics at Penn State, and the SDSS-III Survey coordinator. "The DR9 map already is enabling astronomers to place ever-stronger constraints on the evolutionary history of the universe."

Data Release 9 is the latest in a series of SDSS data releases stretching back to 2001. This release includes new data from the ongoing SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), led by David Schlegel of Lawrence Berkeley National Laboratory, which eventually will measure the positions of 1.5-million massive galaxies, as well as 160,000 quasars -- giant black holes actively feeding on stars and gas. "Given that these massive galaxies and quasars are particularly luminous, we can identify them to distances of billions light years from Earth, and hence have direct information about the conditions present in the universe billions of years in the past," said Niel Brandt, distinguished professor of astronomy and astrophysics at Penn State. "This information allows us to determine how the universe expanded during this era, and to determine the relative amounts of dark matter and dark energy present at various times."

That map of the universe is the centerpiece of the DR9 data. The release includes images of 200 million galaxies and spectra of 1.35 million galaxies, including new spectra of 540,000 galaxies whose light reveals how they looked when the universe was half its present age. Spectra show how much light a galaxy gives off at different wavelengths. Because this light is shifted to longer, redder, wavelengths as the universe expands, spectra allow scientists to figure out how much the universe has expanded since the light left each galaxy. The galaxy images, plus these measurements of expansion, are combined by SDSS-III scientists to create the three-dimensional map released with DR9.

"What really makes me proud of this survey is our commitment to creating a legacy for the future," said Michael Blanton, a professor at New York University who led the team that prepared Data Release 9. "Our goal is to create a catalog that will be used long after we are done."

In addition to the cosmological investigations, the DR9 data also provide insights about our own cosmic backyard, the Milky Way galaxy. "The data release contains detailed information, such as location, temperatures, velocities and compositions for more than half a million galactic stars," said Suvrath Mahadevan, assistant professor of astronomy and astrophysics at Penn State. "From an analysis of these data we have found that the Milky Way has been an active cannibal, absorbing smaller galaxies, and this appears to be an ongoing process."

All these new images and spectra contain the promise of new discoveries about our universe during the remaining four years of this SDSS-III survey. "This project is science at its collaborative best," said Michael Wood-Vasey, a professor at the University of Pittsburgh and the scientific spokesperson for the SDSS-III collaboration. "SDSS-III scientists work together to address big questions extending from our own galaxy to distant reaches of the universe, and then they share all of that data with the world to allow anyone to make the next big discovery."

All the new data are available now on the Data Release 9 website at online. The SkyServer website at includes lesson plans for teachers who use DR9 data to teach astronomy and other topics in science, technology and math. The DR9 data also will feature in a new release of the Galaxy Zoo citizen science project at online, which will allow online volunteers to contribute to cutting-edge astronomy research.

  • Galaxies are concentrated into clusters and filaments with voids in between. The SDSS-III is exploring this structure to determine the nature of dark energy and the distribution of dark matter in the Universe.

    IMAGE: Yushu Yao and Prabhat (Lawrence Berkeley National Laboratory, NERSC), Miguel A. Aragon (Johns Hopkins University), and the SDSS-III Collaboration
Last Updated August 10, 2012