The Sloan Digital Sky Survey has released a comprehensive analysis of the largest three-dimensional map of the universe ever created, filling in the most significant gaps in our exploration of its history.
The Sloan Digital Sky Survey (SDSS) has released a comprehensive analysis of the largest three-dimensional map of the universe ever created, filling in the most significant gaps in our exploration of its history.
“This work, the culmination of two decades of analysis, provides the best measurements yet of how the universe has expanded over the last 11 billion years,” says Michael Blanton, a professor of physics at New York University and director of the SDSS-IV project. “It shows at the highest precision yet that the universe’s expansion seems to be accelerating due to a ‘cosmological constant,’ sometimes referred to as ‘dark energy.'”
“We know both the ancient history of the universe and its recent expansion history fairly well, but there’s a troublesome gap in the middle 11 billion years,” adds cosmologist Kyle Dawson of the University of Utah, who led the team within SDSS announcing the new results. “For five years, we have worked to fill in that gap, and we are using that information to provide some of the most substantial advances in cosmology in the last decade.”
SDSS-IV was launched in 2012. It has sought, in part, to capture more precise cosmological measurements of this gap in cosmic history through the extended Baryon Oscillation Spectroscopic Survey (eBOSS), which produced the new analysis. The work of eBOSS, an international collaboration of more than 100 astrophysicists, yields detailed measurements of more than two million galaxies and quasars covering 11 billion years of cosmic time.
The analysis deployed redshift surveys, which gauge the speeds at which galaxies move away from Earth due to the universe’s expansion, in order to infer their distances.
“This latest result is a game-changer in that it uses different types of galaxies that have not been observed in large-scale redshift surveys,” notes Jeremy Tinker, an assistant professor in NYU’s Department of Physics, who led the selection of the galaxies and quasars to observe for eBOSS. “These galaxies allow us to make maps of the universe that go deeper and larger than ever before possible. We can now go back and map the universe at a time when it was only half its present size and less than half its age.”
An SDSS map is shown as a rainbow of colors, located within the observable universe. The center of the map represents Earth at the present moment–the place from which we are looking out to see the universe. The inset for each color-coded section of the map includes an image of a typical galaxy or quasar from that section and also the signal of the pattern. As we look out in distance, we look back in time, meaning the location of these signals reveals the expansion rate of the universe at different times in cosmic history. Image Credit: Anand Raichoor (EPFL), Ashley Ross (Ohio State University) and the SDSS Collaboration
Scientists have known what the universe looked like in its infancy due to previous measurements of elements created soon after the Big Bang as well as analyses of the Cosmic Microwave Background-a remnant of the early stages of the universe. The universe’s expansion history over the last few billion years has also been documented-from galaxy maps and distance measurements, including those from previous phases of the SDSS.
“Taken together, detailed analyses of the eBOSS map and the earlier SDSS experiments have now provided the most accurate expansion history measurements over the widest-ever range of cosmic time,” observes Will Percival of the University of Waterloo, eBOSS’s Survey Scientist. “These studies allow us to connect all these measurements into a complete story of the expansion of the universe.”
The final map reveals the filaments and voids that define the structure in the universe, starting from the time when the universe was only about 300,000 years old. From this map, researchers measure patterns in the distribution of galaxies, which give several key parameters of our universe to better than one percent accuracy, the scientists report.
This map represents the combined effort of more than 20 years of mapping the universe using the Sloan Foundation telescope. The cosmic history that has been revealed in this map shows that about six billion years ago, the expansion of the universe began to accelerate and has continued to get faster and faster ever since.
Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the participating institutions, including NYU. For more, please visit the SDSS web site at www.sdss.org.
