Astrophysicists and cosmologists from the Sloan Digital Sky Survey (SDSS) have released the largest 3D map of the Universe ever created, filling in the most significant gaps in our exploration of its history. At the heart of the new results are detailed measurements of more than two million galaxies and quasars covering 11 billion years of cosmic time. The new map comes from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), an SDSS collaboration of more than 100 astrophysicists worldwide, and represents the combined effort of more than 20 years of mapping the Universe using the Sloan Foundation Telescope at Apache Point Observatory.
The eBOSS map is shown as a rainbow of colors, located within the observable Universe (the outer sphere, showing fluctuations in the Cosmic Microwave Background). We are located at the center of this map. 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 that the eBOSS team measures there. As we look out in distance, we look back in time. So, the location of these signals reveals the expansion rate of the Universe at different times in cosmic history. Imager credit: Anand Raichoor, EPFL / Ashley Ross, Ohio State University / SDSS Collaboration.
“This is one of the most substantial advances in cosmology in the last decade,” said Professor Will Percival, a researcher at the University of Waterloo and Perimeter Institute.
“Over the last 20 years, the SDSS has created a series of surveys that now span a period of 11 billion years of cosmic history.”
“We have worked to fill in that gap, and we are now using that information to gain a better understanding of this period in our Universe.”
“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,” said Dr. Kyle Dawson, a cosmologist at the University of Utah.
“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.”
A close look at the eBOSS 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, astrophysicists measure patterns in the distribution of galaxies, which give several key parameters of our Universe to better than one percent accuracy.
The cosmic history that has been revealed in this map shows that about 6 billion years ago, the expansion of the Universe began to accelerate, and has continued to get faster and faster ever since.
This accelerated expansion seems to be due to dark energy, consistent with Albert Einstein’s general theory of relativity but extremely difficult to reconcile with our current understanding of particle physics.
Combining observations from eBOSS with studies of the Universe in its infancy reveals cracks in this picture of the Universe.
In particular, the team’s measurement of the current rate of expansion of the Universe — the so-called Hubble constant — is about 10 % lower than the value found from distances to nearby galaxies.
The high precision of the eBOSS data means that it is highly unlikely that this mismatch is due to chance, and the rich variety of eBOSS data gives us multiple independent ways to draw the same conclusion.
“Only with maps like ours can you actually say for sure that there is a mismatch in the Hubble constant,” said Dr. Eva-Maria Mueller, a scientist at the University of Oxford.
“These newest maps from eBOSS show it more clearly than ever before.”
“Thanks to these maps, my colleagues and I were able to observe and study how fast the Universe was expanding and how fast structures formed,” added Dr. Julian Bautista, a researcher in the Institute of Cosmology and Gravitation at the University of Portsmouth.
To create the part of the map dating back 6 billion years, the team used large, red galaxies. Farther out, they used younger, blue galaxies. Finally, to map the Universe 11 billion years in the past and more, they used quasars, which are bright galaxies lit up by material falling onto a central supermassive black hole.
“Quasars provide a unique sample that allows us to bridge the redshift gap between galaxies and the Lyman-alpha forest at the highest redshifts,” said Dr. Jiamin Hou, a researcher at the Max Planck Institute for Extraterrestrial Physics.
“With galaxies we can look back over the last few billion years of cosmic history, the quasars take us back about 10 billion years, and finally the Lyman-alpha galaxies allow us to look back to when the Universe was less than 2 billion years old.”
Each of the samples required careful analysis in order to remove contaminants, and reveal the patterns of the Universe.
“By combining eBOSS data with additional data from the Cosmic Microwave Background, supernovae, and other programs, we can simultaneously measure many fundamental properties of the Universe,” Dr. Mueller said.
“The eBOSS data cover such a large swath of cosmic time that they provide the biggest advances of any probe to measure the geometrical curvature of the Universe, finding it to be flat. They also allow measurements of the local expansion rate to better than one percent.”
“In 2012, I launched the eBOSS project with the idea of producing the most complete 3D map of the Universe throughout the lifetime of the Universe, implementing for the first time celestial objects that indicate the distribution of matter in the distant Universe, galaxies that actively form stars and quasars,” said Professor Jean-Paul Kneib, Director of the Laboratory of Astrophysics at the Ecole Polytechnique Fédérale de Lausanne (EPFL).
“It is a great pleasure to see the culmination of this work today.”
The team’s results will be published in a series of 20 papers in the Monthly Notices of the Royal Astronomical Society.
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This article is based on a press-release provided by the Sloan Digital Sky Survey.
