Quasars illustrate dark energy's roller coaster ride. 13 November 2012Last updated at 03:29 ET By Jonathan Amos Science correspondent, BBC News BOSS data is acquired by the 2.5m Sloan telescope at Apache Point Observatory in the US Scientists have used a novel technique to probe the nature of dark energy some 10 billion years into the past.
They hope it will bring them closer to an explanation for the strange force that appears to be driving the Universe apart at an accelerating rate. The method relies on bright but distant objects known as quasars to map the spread of hydrogen gas clouds in space. The 3D distribution of these clouds can be used as a tracer for the influence of dark energy through time. A scholarly paper describing the approach has been submitted to the journal Astronomy & Astrophysics and posted on the arXiv.org preprint site. It is authored by the BOSS (Baryon Oscillation Spectroscopic Survey) team, which uses the 2.5m Sloan Foundation Telescope in New Mexico, US, to make its observations of the sky. Universe 'expanding like a rollercoaster' BOSS quasars unveil a new era in the expansion history of the universe.
BOSS, the Baryon Oscillation Spectroscopic Survey, is mapping a huge volume of space to measure the role of dark energy in the evolution of the universe.
BOSS is the largest program of the third Sloan Digital Sky Survey (SDSS-III) and has just announced the first major result of a new mapping technique, based on the spectra of over 48,000 quasars with redshifts up to 3.5, meaning that light left these active galaxies up to 11.5 billion years in the past. "No technique for dark energy research has been able to probe this ancient era before, a time when matter was still dense enough for gravity to slow the expansion of the universe, and the influence of dark energy hadn't yet been felt," says BOSS principal investigator David Schlegel, an astrophysicist in the Physics Division of the U.S.
Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab). "In our own time, expansion is accelerating because the universe is dominated by dark energy. BOSS Quasars Unveil a New Era in the Expansion History of the Universe. News Release Light from distant quasars (red dots at left) is partially absorbed as it passes through clouds of hydrogen gas.
A “forest” of hydrogen absorption lines in an individual quasar’s spectrum (inset) pinpoints denser clumps of gas along the line of sight, and the spectra are collected by the telescope’s spectrograph (square at right). The accessible redshift range corresponds on average to about 10 billion years ago. While the Sloan Digital Sky Survey had previously collected spectra from some quasars in this range, by measuring 10 times as many per square degree of sky BOSS can reconstruct a three-dimensional map of the otherwise invisible gas, revealing the large-scale structure of the early universe.
(Illustration by Zosia Rostomian, Lawrence Berkeley National Laboratory; Nic Ross, BOSS Lyman-alpha team, Berkeley Lab; and Springel et al, Virgo Consortium and Max Planck Institute for Astrophysics) (Click on image for best resolution) Two ways to measure the expanding universe.