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).
"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."
Dark energy is the unknown something that appears to account for almost three-quarters of the mass-energy of the universe and is the cause of its accelerating expansion. The discovery of the accelerating universe, announced in 1998 by two teams, resulted in the 2011 Nobel Prize in Physics, divided between Berkeley Lab and UC Berkeley astrophysicist Saul Perlmutter, leader of the Supernova Cosmology Project, and Brian Schmidt and Adam Riess of the competing High‑z Supernova Search team.
"After we won the Nobel Prize, the question we all heard most was, 'Now that you've discovered dark energy, what comes next?'" says Perlmutter, who is the Executive Director of the BCCP as well as principal investigator for the Moore Foundation's BigBOSS grant. "The answer is pretty clear: we have to find out what dark energy is. There's no end of theories. To know which are possible, what we need most is the kind of accurate observational evidence that only BigBOSS and other advanced experiments can give us."
BigBOSS program director Michael Levi says, "BigBOSS represents the next big leap, to the highest level of gain in understanding the mystery of dark energy. With BigBOSS, Berkeley Lab and NOAO" – the National Science Foundation's National Optical Astronomical Observatory – "were the first to present a detailed, practical plan for a next-generation, wide-field spectrographic instrument to address these fundamental questions in cosmology."
BigBOSS would measure "baryon acoustic oscillations" (BAO) – regular variations in the density of mass in the universe – which are evident in the netlike tendrils and voids of visible galaxies and intergalactic gas. Ordinary matter adds up to only five percent of the mass-energy in the universe, but its large-scale distribution maps underlying invisible dark matter, another 20 percent of the total, and echoes the minute temperature variations of the ancient cosmic microwave background radiation (CMB). Thus BAO's recurring peaks in density, from the CMB to the present, represent marks on a standard ruler of the cosmos that can be used to measure its expansion history from early times until now.
BigBOSS takes its name from BOSS, the Baryon Oscillation Spectroscopic Survey now underway as the largest component of the third Sloan Digital Sky Survey, which is creating a three-dimensional map of a large volume of space using 1.5 million galaxies and tens of thousands of quasars; BOSS has already produced powerful new cosmological results. BigBOSS is designed to be bigger than BOSS in every way, reaching deeper into space and building its map from 24,000,000 galaxies and 2,000,000 quasars across the entire sky of the Northern Hemisphere.
"If we tasked all the telescopes in the world on this project, we wouldn't be able to make such a comprehensive map of the universe in less than 10 years, with existing instruments," says David Schlegel of Berkeley Lab's Physics Division, the principal investigator of BOSS and scientific leader of the BigBOSS project. "We've figured out how to make such a map with a single telescope, the Mayall Telescope, with the right kind of clever instrument."
Installing that right kind of clever instrument will require modifying the existing 4-meter Mayall Telescope, operated by the NOAO on Kitt Peak in Arizona, which currently covers just half a degree of sky (about the diameter of the full moon). The Mayall's field of view will be enlarged to encompass three degrees, and its focal plane will be populated by robotic actuators capable of precisely positioning 5,000 optical fibers simultaneously, so that each single exposure can rapidly capture the light of 5,000 individually focused galaxies or other astronomical objects.
During every exposure, the light from each object is carried by its individual fiber to one of 10 spectrographs. Each spectrograph has three arms, which use dichroic beam splitters to select blue, red, or near-infrared wavelengths in the spectrum, with a separate camera to record each of these ranges of color. A portion of the Moore Foundation grant will be used to help develop the spectrographs, testing BigBOSS's demanding specifications for spot size and spectral resolution, versus the wavelength and position of the optical fiber on the focal plane.
In addition to Perlmutter and Levi, the Moore Foundation grant agreement names Patrick Jelinsky and Michael Sholl of UC Berkeley's Space Sciences Laboratory, who will design the spectrograph and corrector optics for BigBOSS, two of the key technologies funded by the grant. The Moore Foundation was introduced to BigBOSS by BCCP's Seljak through the arrangements of UC Berkeley's Dean of Mathematical and Physical Sciences, Mark Richards.
Seljak remarks that "this seed money is the most important step in demonstrating that BigBOSS would be the best investment for a planned Department of Energy wide-field spectrographic instrument of this kind, as well as for the millions in contributions expected from our international collaborators once we're under way."
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