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BOSS gives clearer view of baryon oscillations

28 January 2013
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In November the Baryon Oscillation Spectroscopic Survey (BOSS) released its second major result of 2012, using 48,000 quasars with redshifts (z) up to 3.5 as backlights to map intergalactic hydrogen gas in the early universe for the first time, as far back as 11,500 million years ago.

As the light from each quasar passes through clouds of gas on its way to Earth, its spectrum accumulates a thicket of hydrogen absorption lines, the “Lyman-alpha forest”, whose redshifts and prominence reveal the varying density of the gas along the line of sight. BOSS collected enough close-together quasars to map the distribution of the gas in 3D over a wide expanse of sky.

The largest component of the third Sloan Digital Sky Survey, BOSS measures baryon acoustic oscillations (BAO) – recurring peaks of matter density that are most evident in net-like strands of galaxies. Initially imprinted in the cosmic microwave background radiation, BAO provide a ruler for measuring the universe’s expansion history and probing the nature of dark energy.

In March 2012, BOSS released its first results on more than 350,000 galaxies up to z = 0.7, or 7000 million years ago. However, only quasars are bright enough to probe the gravity-dominated early universe when expansion was slowing, well before the transition to the present, where dark energy dominates and expansion is accelerating. When complete, BOSS will have surveyed 1.5 million galaxies and 160,000 quasars.

To resolve the nature of dark energy will need even greater precision. The BigBOSS collaboration, which, like BOSS, is led by scientists at Lawrence Berkeley National Laboratory (LBNL), proposes to modify the 4-m Mayall Telescope to survey 24 million galaxies to z = 1.7, plus two million quasars to z = 3.5. The Gordon and Betty Moore Foundation recently awarded a grant of $2.1 million to help fund the spectrograph and corrector optics, two key BigBOSS technologies.

Further reading

Busca et al. 2012 arXiv:1211.2616v1 [astro-ph.CO] submitted to Astronomy & Astrophysics.

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