An international team of astronomers measures the Universe’s deceleration before dark energy took over

The image shows how the team SDSS-III has achieved to measure the distant Universe. The light rays of distant quasar (on the left) are partially absorbed when they go through the clusters of ionized hydrogen gas. When the light reaches the spectrograph of the telescope, a 2.5 metres one from the Sloan Foundation (on the right), some of them have been absorbed leaving a register, making a ‘forest’ of small lines of absorption in the spectrum observed.. Credits: Zosia Rostomian, LBNL; Nic Ross, BOSS Lyman-alpha team, LBNL; Springel et al., Virgo Consortium i Institute for Astrophysics Max Planck.
The image shows how the team SDSS-III has achieved to measure the distant Universe. The light rays of distant quasar (on the left) are partially absorbed when they go through the clusters of ionized hydrogen gas. When the light reaches the spectrograph of the telescope, a 2.5 metres one from the Sloan Foundation (on the right), some of them have been absorbed leaving a register, making a ‘forest’ of small lines of absorption in the spectrum observed.. Credits: Zosia Rostomian, LBNL; Nic Ross, BOSS Lyman-alpha team, LBNL; Springel et al., Virgo Consortium i Institute for Astrophysics Max Planck.
Research
(13/11/2012)
Different astronomical observations have shown that the expansion of the Universe has been speeding up —the Universe is now 14 billion years old—, powered by the mysterious repulsive force known as “dark energy”. But now, thanks to a new technique for measuring the three-dimensional structure of the distant Universe, astronomers from Sloan Digital Sky (SDSS-III), an International collaboration in which some UB researches participate, have made the first measurement of the cosmic expansion rate just three billion years after the Big Bang.
The image shows how the team SDSS-III has achieved to measure the distant Universe. The light rays of distant quasar (on the left) are partially absorbed when they go through the clusters of ionized hydrogen gas. When the light reaches the spectrograph of the telescope, a 2.5 metres one from the Sloan Foundation (on the right), some of them have been absorbed leaving a register, making a ‘forest’ of small lines of absorption in the spectrum observed.. Credits: Zosia Rostomian, LBNL; Nic Ross, BOSS Lyman-alpha team, LBNL; Springel et al., Virgo Consortium i Institute for Astrophysics Max Planck.
The image shows how the team SDSS-III has achieved to measure the distant Universe. The light rays of distant quasar (on the left) are partially absorbed when they go through the clusters of ionized hydrogen gas. When the light reaches the spectrograph of the telescope, a 2.5 metres one from the Sloan Foundation (on the right), some of them have been absorbed leaving a register, making a ‘forest’ of small lines of absorption in the spectrum observed.. Credits: Zosia Rostomian, LBNL; Nic Ross, BOSS Lyman-alpha team, LBNL; Springel et al., Virgo Consortium i Institute for Astrophysics Max Planck.
Research
13/11/2012
Different astronomical observations have shown that the expansion of the Universe has been speeding up —the Universe is now 14 billion years old—, powered by the mysterious repulsive force known as “dark energy”. But now, thanks to a new technique for measuring the three-dimensional structure of the distant Universe, astronomers from Sloan Digital Sky (SDSS-III), an International collaboration in which some UB researches participate, have made the first measurement of the cosmic expansion rate just three billion years after the Big Bang.
"If we think of the Universe as a roller coaster, then today we are rushing downhill, gaining speed as we go”, says Nicolas Busca from the AstroParticle and Cosmology laboratory of the French National Centre for Scientific Research (CNRS), the main author of the study. “This new measurement tells us about the time when the Universe was climbing the hill, still being slowed by gravity”.
 
The results were presented in a paper published today on the digital repository arXiv and submitted to the journal Astronomy and Astrophysics. In this study the following two researchers have participated in the study: Jordi Miralda, ICREA researcher at the Institute of Cosmos Sciences of the University of Barcelona (ICCUB), and Andreu Font, researcher at the Lawrence Berkeley National Laboratory (University of California). Font, who made his doctoral thesis at the UB, collaborated in the simulations of every observation made in order to calculate the errors in the measurements and to remove different systematic errors from the observations.  
 
New findings are based on data from the Baryon Oscillation Spectroscopic Survey (BOSS), one of the projects included in the collaboration SDSS-III. It uses a technique based on measuring the so-called “baryon acoustic oscillations” (BAO), the acoustic waves propagated in the Early Universe through matter which signal the small variations of density produced at the beginning of the Universe.
 
In a previous work, the SDSS-III presented some results which indicated the galaxiesʼ distribution in the Universe. Today, the data has been obtained from the absorption spectrum of quasars, the brightest objects of the Universe.
 
When we measure the spectrum of a quasar, we see not only the light emitted by the quasar, but also what happened to that light in its long journey to Earth. So, when we look at a quasar's spectrum, we can see how the intervening gas absorbs some of the quasar's light. This spectrum ensemble and its measuring yield a detailed picture of the intergalactic gas between us and the quasar.
 
The SDSS-III team's new measurement of the BAO peak (of these acoustic waves), combined with measurements of the same peak at other points in the Universe's history, paints a picture of how the Universe has evolved over its history. The picture that emerges is consistent with our current understanding of the Universe: dark energy is a constant part of space throughout the cosmos. What is fascinating about the new result is that, for the first time, we see how dark energy worked at a time before the Universe's current acceleration started.
 
According to Miralda, “The great number of quasars observed is the novelty of BOSS experiment. Before it, we only had measured a few thousand, but now we have measured 60,000. This fact allows us to have enough data to rebuild the three-dimensional map of the Universe and to observe the BAO waves. In addition, they are detected for the first time at such a great distance, when the Universe was only 3 billion years old”.

 

Article:

SDSS-III Press Release: http://www.sdss3.org/