## From Brookhaven Lab: “Astronomers from the Sloan Digital Sky Survey Make the Most Precise Measurement Yet of the Expanding Universe”

Brookhaven Lab

April 7, 2014
Contacts: Chelsea Whyte, (631) 344-8671 or Peter Genzer, (631) 344-3174

Astronomers from the Sloan Digital Sky Survey have used 140,000 distant quasars to measure the expansion rate of the Universe when it was only one-quarter of its present age. This is the best measurement yet of the expansion rate at any epoch in the last 13 billion years.

“Quasars in BOSS measure the expansion history of the universe just before the dark energy should have kicked in. If there is funny business going on in the universe at that time, we should be able to detect that!”
— Anže Slosar

The Baryon Oscillation Spectroscopic Survey (BOSS), the largest component of the third Sloan Digital Sky Survey (SDSS-III), pioneered the technique of measuring the structure of the young Universe by using quasars to map the distribution of intergalactic hydrogen gas. Today, new BOSS observations of this structure were presented at the April 2014 meeting of the American Physical Society in Savannah, GA.

These latest results combine two different methods of using quasars and intergalactic gas to measure the rate of expansion of the Universe. The first analysis, by Andreu Font-Ribera (Lawrence Berkeley National Laboratory) and collaborators, compares the distribution of quasars to the distribution of hydrogen gas to measure distances in the Universe. A second analysis team led by Timothée Delubac (Centre de Saclay, France) focused on the patterns in the hydrogen gas itself to measure the distribution of mass in the young Universe. Together the two BOSS analyses establish that 10.8 billion years ago, the Universe was expanding by one percent every 44 million years.

Brookhaven’s Role in the BOSS Findings

Brookhaven cosmologists Erin Sheldon and Anže Slosar made significant contributions to the recent BOSS results.

Erin Sheldon was instrumental in making sure that the experiment observed the correct objects in the sky. In every field of view of the telescope, there are hundreds of thousands of celestial objects that can be observed, but the instrument can look at only 1000 objects at a time. Sheldon and collaborators selected appropriate targets for the telescope, including galaxies and quasars that reside in the cosmos at a distance useful for determining what is driving the expansion of the universe.

“It’s fun to see all our years of groundwork lead to such beautiful and interesting results,” Sheldon said.

Anže Slosar is a senior author on both papers and led one of the two analyses that discovered the baryon acoustic oscillations a year ago.

“These measurements are a real improvement over what we had only a few months ago, so it is amazing to see how fast the field progresses,” he said. “Everybody hopes that one day we will see definite evidence that dark energy is not a static vacuum energy, but something more dynamic.”

Dark energy is the mysterious force that cosmologists hypothesize is driving the accelerating expansion of the universe. “Quasars in BOSS measure the expansion history of the universe just before the dark energy should have kicked in,” Slosar said. “If there is funny business going on in the universe at that time, we should be able to detect that!”

“If we look back to the Universe when galaxies were three times closer together than they are today, we’d see that a pair of galaxies separated by a million light-years would be drifting apart at a speed of 68 kilometers per second as the Universe expands,” says Font-Ribera.

Delubac explains that “we have measured the expansion rate in the young Universe with an unprecedented precision of 2 percent.” Measuring the expansion rate of the Universe over its entire history is key in determining the nature of the dark energy that is responsible for causing this expansion rate to increase during the past six billion years. “By probing the Universe when it was only a quarter of its present age, BOSS has placed a key anchor to compare to more recent expansion measurements as dark energy has taken hold,” says Delubac.

BOSS determines the expansion rate at a given time in the Universe by measuring the size of baryon acoustic oscillations (BAO), a signature imprinted in the way matter is distributed, resulting from sound waves in the early Universe. This imprint is visible in the distribution of galaxies, quasars, and intergalactic hydrogen throughout the cosmos.

“Three years ago, BOSS used 14,000 quasars to demonstrate we could make the biggest 3-D maps of the Universe,” says David Schlegel (Lawrence Berkeley National Laboratory), principal investigator of BOSS. “Two years ago, with 48,000 quasars, we first detected baryon acoustic oscillations in these maps. Now, with more than 140,000 quasars, we’ve made extremely precise measures of BAO.”

As the light from a distant quasar passes through intervening hydrogen gas distributed throughout the Universe, patches of greater density absorb more light. Each absorbing patch absorbs light from the spectrum of the quasar at a characteristic wavelength of neutral hydrogen. As the Universe expands, the quasar spectrum is stretched out, and each subsequent patch leaves its absorption mark at a different relative wavelength. The quasar spectrum is finally observed on Earth by BOSS, and it contains the signatures of all the patches encountered by the quasar light. Astronomers then measure from the quasar spectrum how much the Universe has expanded since the light passed through each patch of hydrogen.

With enough good quasar spectra, close enough together, the position of the gas clouds can be mapped in three dimensions. BOSS determines the expansion rate by using these maps to measure the size of the BAO pattern at different epochs of cosmic time. These new measurements provide key data for astronomers seeking the nature of the dark energy postulated to be driving the increase in the expansion rate of the Universe.

David Schlegel remarks that when BOSS was first getting underway, precision measurements using quasars and the Lyman-alpha forest had been suggested, but “som\begin{equi}

\end{equi}e of us were afraid it wouldn’t work. We were wrong. Our precision measurements are even better than we optimistically hoped for.”

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. This research used resources of the National Energy Research Scientific Computing Center (NERSC), which is supported by the Office of Science. Visit SDSS-III at http://www.sdss3.org.

SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, University of Cambridge, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University.
Contacts
Andreu Font-Ribera, Lawrence Berkeley National Laboratory, afont@lbl.gov, 1-510-332-0635
Timothee Delubac, Ecole Polytechnique Federale de Lausanne (Switzerland), timothee.delubac@epfl.ch, +44 22 379 2474
David Schlegel, Lawrence Berkeley National Laboratory, djschlegel@lbl.gov, 1-510-495-2595
Michael Wood-Vasey, SDSS-III Spokesperson, University of Pittsburgh, wmwv@pitt.edu, 1-412-624-2751

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

## From Berkeley Lab: “Gordon and Betty Moore Foundation Gives a Big Boost to BigBOSS”

$2.1 Million Grant to Berkeley Center for Cosmological Physics advances dark energy research at UC Berkeley and Berkeley Lab December 04, 2012 Paul Preuss “A$2.1 million grant from the Gordon and Betty Moore Foundation to the University of California at Berkeley, through the Berkeley Center for Cosmological Physics (BCCP), will fund the development of revolutionary technologies for BigBOSS, a project now in the proposal stage designed to study dark energy with unprecedented precision. BigBOSS is based at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab).

The BigBOSS proposal adds a new widefield, prime-focus corrector to the Mayall 4-meter telescope. A focal array with 5,000 optical fibers, individually positioned by robotic actuators, delivers light to a set of 10 three-arm spectrometers. (Lawrence Berkeley National Laboratory. Background photo Mark Duggan)

‘BigBOSS is the next big thing in cosmology,’ says Uroš Seljak, Director of the BCCP, who is a professor of physics and astronomy at UC Berkeley and a member of Berkeley Lab’s Physics Division. ‘It would map millions and millions of galaxies, allowing us to measure dark energy to high precision – and would yield other important scientific results as well, including determining neutrino mass and the number of neutrino families.’”

A U.S. Department of Energy National Laboratory Operated by the University of California

## From Symmetry: “Spectroscopy – explain it in 60 seconds”

Illustration: Sandbox Studio, Chicago; Image courtesy of: ESA/Hubble & NASA

February 18, 2013
Klaus Honscheid and Eric Huff, Center for Cosmology and AstroParticle Physics, The Ohio State University

Spectroscopy is a technique that astronomers use to measure and analyze the hundreds of colors contained in the light emitted by stars, galaxies and other celestial objects.

Analysis of white light by dispersing it with a prism is an example of spectroscopy

“Ordinary telescopes show the directions in which objects are located but offer no information on how far away these objects are.

Spectroscopic surveys make use of the fact that, as light travels to us from distant galaxies, it gets stretched out by the expanding universe and appears redder. By measuring the light spectrum of a galaxy, scientists can determine its redshift and thus its distance.

The largest spectroscopic survey to date is the Baryon Oscillation Spectroscopic Survey, which is being carried out at the Sloan telescope and will record the spectra of 1.5 million galaxies by the time it’s completed in 2014. BOSS will offer insight into one of the biggest mysteries of the universe: dark energy, the enigmatic force that has accelerated the universe’s expansion over the last 5 billion years.

The Sloan Foundation 2.5-m Telescope at the Apache Point Observatory

An even more ambitious spectroscopic survey to measure the redshifts of 20 million galaxies is now being developed. In a few years, when this new spectroscopic survey experiment goes online, we will finally realize the massive scale of cosmic cartography necessary for truly sensitive measurements of dark energy.”

See the original article here.

You can explore the full explain it in 60 seconds archive. It is worth your time.

Symmetry is a joint Fermilab/SLAC publication.

## From Symmetry: “Scientists propose new projects to unravel dark energy secrets”

Scientists have risen to the challenge to design an experiment that will make measurements of millions of galaxies to probe dark energy in new ways.

December 05, 2012
Jessica Orwig

About 5 billion years ago the universe underwent a crucial transition. The gravitational tug that pulled together the matter in the universe was overwhelmed by a different, repulsive phenomenon. As a result, the universe began to expand at an accelerating rate. Scientists have given that phenomenon a name: dark energy. However, they can say with confidence only what it does, not what it is, where it comes from, or why it’s pushing galaxies apart at an ever more rapid speed.

Courtesy of: Sloan Digital Sky Survey

The Department of Energy recently declared the need to construct a powerful new device that scientists could use to address fundamental questions about dark energy. Scientists have proposed two different projects to fulfill this need. The projects aim to study the three-dimensional distribution and motions of galaxies before and after the transition epoch between the matter-dominated and dark-energy-dominated eras.

In the northern hemisphere, the proposed BigBOSS project would attach a spectroscopic instrument to the Mayall telescope atop Kitt Peak in southern Arizona. BigBOSS is a scaled up version of the BOSS spectroscopic survey. In the southern hemisphere, the proposed DESpec project would attach a spectroscopic instrument to the Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile, current home of the Dark Energy Survey. Lawrence Berkeley National Laboratory is the headquarters for the BigBOSS project, while Fermilab heads the design of DESpec.

BigBoss/BigBoss3/4-Meter Optical

Both of these projects would, in different ways, construct the largest three-dimensional maps of the cosmos ever made by collecting spectra of millions of galaxies—many times more than any previous spectroscopic survey.

Symmetry is a joint Fermilab/SLAC publication.

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