The largest ever three-dimensional map of massive galaxies and distant black holes has been published by the Sloan Digital Sky Survey III, or SDSS-III, with help from the University of Arizona. It will bring astronomers closer to explaining the mysterious dark matter and dark energy believed to make up 96 percent of the universe.
Early last year, the SDSS-III released the largest ever image of the sky. With the new release of data, SDSS-III has begun to expand this image into a full three-dimensional map. Data Release 9, or DR9, posted online last week, makes available the first one-third of the galaxy map that this six-year project will create.
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.
"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 DR9. "Our goal is to create a map of the universe that will be used long after we are done by future generations of astronomers, physicists and the general public."
Data Release 9 is the latest in a series of data releases stretching back to 2001. This release includes new data from the ongoing SDSS-III Baryon Oscillation Spectroscopic Survey
, which eventually will measure the positions of 1.5 million massive galaxies over the past 6 billion years of cosmic time, as well as 160,000 quasars – giant black holes actively feeding on stars and gas – from as long ago as 12 billion years in the past.
"A unique feature of this data release is the publication of the position and distance of more than 80,000 quasars between 10 and 12 billion light years away," said Xiaohui Fan
, a professor of astronomy at the UA Steward Observatory
who was involved in the mapping effort. "This allows us to map the universe when it was only about one-quarter of its current age and probe the cosmic evolution of dark energy and dark matter across cosmic time."
With such a map, scientists can retrace the history of the universe over the last 6 billion years. With that history, they can get better estimates for how much of the universe is made up of dark matter – matter that we can't directly see because it doesn't emit or absorb light – and dark energy, the even more mysterious force that drives the accelerating expansion of the universe.
"Dark matter and dark energy are two of the greatest mysteries of our time," said David Schlegel of Lawrence Berkeley National Laboratory, who led the SDSS-III effort to map these galaxies and quasars. "We're confident this new map will guide us, or someone else, in solving these mysteries."
That map of the universe is the centerpiece of DR9. It includes new spectra from 540,000 galaxies from when the universe was half its present age. A spectrum is a measure of light from a galaxy at different wavelengths; from this information we can measure the distances to those galaxies. This distance information provides the third dimension in the DR9 map, providing a more detailed view of the structure of the universe than has been measured before.
Quasars provide further details to the three dimensional map and another way to measure the distribution of matter in the universe. Quasars are the brightest objects in the distant universe, and their spectra reveal intricate patterns imprinted by the intergalactic gas and underlying dark matter that lies between each quasar and the Earth.
The new data in DR9 not only are helping us understand the distant universe, but also our own cosmic backyard, the Milky Way galaxy. DR9 includes better estimates for the chemical compositions of more than a half-million stars in our own galaxy.
"With these better estimates, we can look back at the history of our galaxy," said Connie Rockosi of the University of California Santa Cruz, who leads the SDSS- III's Milky Way study. "This new information can help us tell the story of how our galaxy formed and how it came to be the Milky Way that we see today."
All these new images and spectra contain the promise of new discoveries about our universe – but the SDSS-III is only in the middle of its six-year survey, and will release three times as much data by the time it's completed in 2014.
"The most fun part of making this data available online is knowing that anyone on the Internet can now access the very same data and search tools that professional astronomers use to make exciting discoveries about our universe," said Ani Thakar of Johns Hopkins University, a key member of the data team who works hard behind the scenes to distribute the terabytes of SDSS-III data to astronomers and the public through these data releases.
All the data are available now on the DR9 website. The new data are being made available to astronomers as well as students, teachers and the public. The SkyServer website includes lesson plans for teachers that use DR9 data to teach astronomy and other topics in science, technology and math. DR9 data will also feature in a new release of the Galaxy Zoo citizen science project, which will allow online volunteers to contribute to cutting-edge astronomy research.
Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation and the U.S. Department of Energy’s Office of Science.