- Number 298 |
- October 26, 2009
BOSS begins most ambitious baryon oscillation search yet
BOSS, the Baryon Oscillation
BOSS, the Baryon Oscillation Spectroscopic Survey, is the most ambitious attempt yet to map the expansion history of the Universe using the technique known as baryon acoustic oscillation (BAO). The largest of four surveys in the Sloan Digital Sky Survey-III, the BOSS collaboration is led by scientists with the Physics Division of DOE's Lawrence Berkeley National Laboratory, including principal investigator David Schlegel, survey scientist Martin White, and instrument scientist Natalie Roe. BOSS achieved “first light” on the night of September 14-15, when it acquired data with an upgraded spectrographic system across the entire focal plane of the Sloan Foundation’s 2.5-meter telescope at Apache Point Observatory in New Mexico. In the next five years BOSS will measure 1.4 million luminous red galaxies at redshifts up to 0.7 (when the Universe was roughly seven billion years old) and 160,000 quasars at redshifts between 2.0 and 3.0 (when the Universe was only about three billion years old). BOSS will also measure variations in the density of hydrogen gas between the galaxies.
Daniel Eisenstein of the University of Arizona is the director of SDSS-III.
“Baryon oscillation is a fast-maturing method for measuring dark energy in a way that’s complementary to the proven techniques of supernova cosmology,” says Schlegel. “The data from BOSS will be some of the best ever obtained on the large-scale structure of the Universe.”
BOSS’s first exposure was made after many nights of clouds and rain in the Sacramento Mountains when spectroscopy was obtained of some 800 galaxies and 200 quasars in the constellation Aquarius. Team member Vaishali Bhardwaj, a graduate student at the University of Washington fresh from a summer internship at Berkeley Lab, helped operate the telescope. Bhardwaj’s teammate, Berkeley Lab postdoc Nic Ross, quipped that given the constellation where first light was obtained, the accomplishment marked the “dawning of the Age of Aquarius.”
Measuring baryon oscillations
Baryon oscillations began as pressure waves propagated through the hot plasma of the early universe, creating regions of varying density that can be read today as temperature variations in the cosmic microwave background. The same density variations left their mark as the Universe evolved, in the periodic clustering of visible matter in galaxies, quasars, and intergalactic gas, as well as in the clumping of invisible dark matter.
Comparing these scales at different eras makes it possible to trace the details of how the Universe has expanded throughout its history—information that can be used to distinguish among competing theories of dark energy.
[Paul Preuss, 510.486.6249 ,