BOSS survey probes early universe

Posted by Kate Taylor

Scientists using BOSS, the Baryon Oscillation Spectroscopic Survey, have used a new mapping technique to probe the period before dark energy began to speed up the expansion of the universe.

The team has examined the spectra of over 48,000 quasars with redshifts up to 3.5, meaning that light left them up to 11.5 billion years ago.



BOSS studies dark energy by mapping baryon acoustic oscillations (BAO) - the large-scale network of variations in the distribution of visible galaxies and clouds of intergalactic gas, which also reveal the presence of dark matter.

The regular spacing of peaks in matter density originated in primordial density variations, and provide a cosmic ruler for calibrating the rate of expansion wherever BAO can be measured.

The BOSS team is focusing on quasars.


As the light of a quasar passes through clouds of intergalactic gas on its way to Earth, its spectrum develops a plethora of hydrogen absorption lines known as a Lyman-alpha forest. Ideally, each absorption line in the 'forest' reveals where the quasar's light has passed through an intervening gas cloud, showing how gas density varies with distance along the line of sight.


"We don't use the specific information in a single line of sight, we look at the correlations among many," says Berkeley Lab's Bill Carithers. "BOSS is the first to do this because we have enough quasars - with too few, you can't see the pattern."


"We are seeing back to the matter-dominated universe, when expansion was decelerating and dark energy was hard to see," says Martin White of Berkeley Lab.
