BOSS: Dark Energy and the Geometry of Space

The SDSS-III's Baryon Oscillation Spectroscopic Survey (BOSS) will map the spatial distribution of luminous galaxies and quasars to detect the characteristic scale imprinted by baryon acoustic oscillations in the early universe. Sound waves that propagate in the early universe, like spreading ripples in a pond, imprint a characteristic scale on cosmic microwave background fluctuations. These fluctuations have evolved into today's walls and voids of galaxies, meaning this baryon acoustic oscillation scale is visible among galaxies today.

A map of luminous red galaxies, as seen by the SDSS. The large red circle shows the characteristic scale of baryon acoustic oscillations.

Using the acoustic scale as a physically calibrated ruler, BOSS will determine the angular diameter distance with a precision of 1% at redshifts z = 0.3 and z = 0.6 and 1.5% at z = 2.5, and it will measure the cosmic expansion rate H(z) with 1-2% precision at the same redshifts. These measurements will provide demanding tests for theories of dark energy and the origin of cosmic acceleration.

For a detailed description of BOSS, see Section 3 of the Project Description, available as a PDF document.

The BAO scale can be seen as a bump in the correlation function of luminous galaxies (inset: close-up of bump).