The SDSS map is shown as a rainbow of colors, located within the observable Universe (the outer sphere, which shows fluctuations in the Cosmic Microwave Background).
We are located in the center of this map. The box for each color-coded section of the map includes an image of a galaxy or quasar typical of that section, and also the pattern signal that the eBOSS team measures there. As we look into the distance, we look back in time. So the location of these signals reveals the rate of expansion of the Universe at different times in cosmic history.
Credit: Anand Raichoor (EPFL), Ashley Ross (Ohio State University) and the SDSS Collaboration
The Sloan Digital Sky Survey (SDSS) released a comprehensive analysis of the largest three-dimensional map of the Universe ever created, filling the most significant gaps in our possible exploration of its history.
“We know the ancient history of the universe and its recent history of expansion quite well, but there is a problematic gap in the middle of 11 billion years,” says cosmologist Kyle Dawson of the University of Utah, who leads the team announcing the today’s results. “For five years, we have worked to fill that gap, and we are using that information to provide some of the most important advancements in cosmology in the past decade.”
“These studies allow us to connect all of these measurements into a complete history of the expansion of the Universe.” – Will Percival
The new results come from the Extended Baryon Oscillation Spectroscopic Study (eBOSS), an international collaboration of more than 100 astrophysicists that is one of the component studies of the SDSS. At the heart of the new results are detailed measurements of more than two million galaxies and quasars that cover 11 billion years of cosmic time.
We know what the Universe was like in its infancy, thanks to the thousands of scientists around the world who have measured the relative amounts of elements created shortly after the big Bang, and who have studied the cosmic microwave background. We also know its history of expansion in the last few billion years from galaxy maps and distance measurements, including those from earlier phases of the SDSS.
Scientists at the Sloan Digital Sky Survey (SDSS) have published a comprehensive analysis of the largest three-dimensional map of the universe ever created. The new results come from the Extended Baryon Spectroscopic Oscillation Study (eBOSS), an SDSS collaboration of more than 100 astrophysicists worldwide. SDSS-IV Director Michael Blanton (New york university) and eBOSS Survey Scientist Will Percival (Perimeter Institute and University of Waterloo) Discuss the legacy of 20 years of SDSS galaxy surveys.
“Taken together, detailed analyzes of the eBOSS map and previous SDSS experiments have now provided the most accurate expansion history measurements in the widest range of cosmic time,” says Will Percival of the University of Waterloo, eBOSS Survey Scientist. . “These studies allow us to connect all of these measurements into a complete history of the expansion of the Universe.”
The final map is shown in the image above. A close look at the map reveals the filaments and gaps that define the structure in the Universe, starting from the time when the Universe was only about 300,000 years old. From this map, the researchers measure patterns in the distribution of galaxies, which give several key parameters of our universe to more than one percent accuracy. The signals of these patterns are shown in the image inserts.
This image illustrates the impact that the eBOSS and SDSS maps have had on our understanding of the current expansion rate and curvature of the Universe in the last 20 years of work.
The gray region shows our knowledge from 10 years ago. The blue region shows the best current measurement, which combines SDSS and other programs. The decreasing sizes of the colored regions show how our knowledge of the expansion rate has improved.
The red region shows the contribution of the SDSS data to this improvement. The measurements of the curvature of the Universe are shown on the horizontal axis. The SDSS results, which focus on zero, suggest that the Universe is flat and significantly improve the limitations of other experiments. The vertical axis shows the current expansion rate of the Universe (the Hubble constant). Measurements from the Hubble Constant from the SDSS and other surveys are inconsistent with measurements from nearby galaxies, which find a value close to 74 in these units, as opposed to 68 for the SDSS. Only with the data taken from SDSS and other experiments in the last decade has it been possible to reveal this discrepancy.
Credit: Eva-Maria Mueller (Oxford University) and the SDSS collaboration
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 on this map shows that about six billion years ago, the expansion of the Universe began to accelerate, and since then it has continued to grow ever faster. This accelerated expansion appears to be due to a mysterious invisible component of the Universe called “dark energy”, consistent with Einstein’s General Theory of Relativity, but extremely difficult to reconcile with our current understanding of particle physics.
Combining eBOSS observations with childhood studies of the Universe reveals cracks in this picture of the Universe. In particular, the eBOSS team’s measurement of the Universe’s current rate of expansion (the “Hubble Constant”) is approximately 10 percent lower than the value found from distances to nearby galaxies. The high precision of the eBOSS data means that this mismatch is highly unlikely to be due to chance, and the wide variety of eBOSS data gives us multiple independent ways to draw the same conclusion.
Scientists at the Sloan Digital Sky Survey (SDSS) have published a comprehensive analysis of the largest three-dimensional map of the universe ever created. The new results come from the Extended Baryon Spectroscopic Oscillation Study (eBOSS), an SDSS collaboration of more than 100 astrophysicists worldwide. They provide detailed measurements of more than two million galaxies and quasars, spanning 11 billion years in our picture of the universe.
EBOSS principal investigator Kyle Dawson (University of Utah), scientific researcher Will Percival (Perimeter Institute and the University of Waterloo), and Jiamin Hou (Max Planck Institute for Extragalactic Physics), discuss the new results, how the eBOSS runs the project and the meaning of the results for our understanding of the universe.
“Only with maps like ours can you say with certainty that there is a mismatch in the Hubble Constant,” says Eva-Maria Mueller of the Oxford University, who led the analysis to interpret the results of the entire SDSS sample. “These latest eBOSS maps show it more clearly than ever.”
There is no widely accepted explanation for this discrepancy in measured expansion rates, but an exciting possibility is that a previously unknown form of matter or energy from the early Universe could have left a trace in our history.
In total, the eBOSS team released the results of more than 20 scientific articles. Those documents describe, in more than 500 pages, the team’s analyzes of the latest eBOSS data, marking the completion of the survey’s key objectives.
Within the eBOSS team, individual groups from universities around the world focused on different aspects of the analysis. To create the part of the map that dates back six billion years, the team used large red galaxies. Further, they used younger blue galaxies. Finally, to map the Universe eleven billion years in the past and beyond, they used quasars, which are bright galaxies lit by material falling on a central supermassive. dungeon. Each of these samples required careful analysis to remove contaminants and reveal patterns in the Universe.
“By combining SDSS data with additional data from the Cosmic Microwave Background, supernovae and other programs, we can simultaneously measure many fundamental properties of the Universe,” says Mueller. “The SDSS data covers such a large swath of cosmic time that they provide the greatest advancement of any probe to measure the geometric curvature of the Universe, finding it to be flat. They also allow measurements of the local expansion rate to more than one percent. “
eBOSS, and SDSS in general, leave the enigma of dark energy and the mismatch of the expansion rate of the local and early Universe, as a legacy for future projects. In the next decade, future surveys may solve the puzzle, or perhaps reveal more surprises.
Meanwhile, with the continued support of the Alfred P. Sloan Foundation and institutional members, the SDSS has nothing to do with its mission to map the Universe. Karen Masters of Haverford College, spokesperson for the current phase of SDSS, described her enthusiasm for the next phase. “The Sloan Foundation telescope and its close twin at Las Campanas Observatory will continue to make astronomical discoveries mapping millions of stars and black holes as they change and evolve with cosmic time.” The SDSS team is busy building the hardware to start this new phase and awaits new discoveries for the next 20 years.
