Find out the latest thinking about our universe.
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MargaritaMc
- Look to the Evenstar
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by MargaritaMc » Tue Apr 08, 2014 11:06 am
LBL: BOSS Quasars Track the Expanding Universe – the Most Precise Measurement Yet
Excerpt from this news release
The Baryon Oscillation Spectroscopic Survey (BOSS), the largest component of the third Sloan Digital Sky Survey (SDSS-III), pioneered the use of quasars to map density variations in intergalactic gas at high redshifts, tracing the structure of the young universe. BOSS charts the history of the universe’s expansion in order to illuminate the nature of dark energy, and new measures of large-scale structure have yielded the most precise measurement of expansion since galaxies first formed.
The latest quasar results combine two separate analytical techniques. A new kind of analysis, led by physicist Andreu Font-Ribera of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and his team, was published late last year. Analysis using a tested approach, but with far more data than before, has just been published by Timothée Delubac, of EPFL Switzerland and France’s Centre de Saclay, and his team. The two analyses together establish the expansion rate at 68 kilometers per second per million light years at redshift 2.34, with an unprecedented accuracy of 2.2 percent.
...
BOSS employs both galaxies and distant quasars to measure baryon acoustic oscillations (BAO), a signature imprint in the way matter is distributed, resulting from conditions in the early universe. ...
*BAO directly descends from pressure waves (sound waves) *moving through the early universe, when particles of light and matter were inextricably entangled; 380,000 years after the big bang, the universe had cooled enough for light to go free. The cosmic microwave background radiation preserves a record of the early acoustic density peaks; these were the seeds of the subsequent BAO imprint on the distribution of matter.
...
The papers referred to in the release are:
http://arxiv.org/abs/1311.1767
Quasar-Lyman α Forest Cross-Correlation from BOSS DR11 : Baryon Acoustic Oscillations
Andreu Font-Ribera, David Kirkby, Nicolas Busca, et al
http://arxiv.org/abs/1404.1801
Baryon Acoustic Oscillations in the Lyα forest of BOSS DR11 quasars
Timothée Delubac, Julian E. Bautista, Nicolás G. Busca, et al
* * I'm puzzled by this - can anyone enlighten me?
Margarita
"In those rare moments of total quiet with a dark sky, I again feel the awe that struck me as a child. The feeling is utterly overwhelming as my mind races out across the stars. I feel peaceful and serene."
— Dr Debra M. Elmegreen, Fellow of the AAAS
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MargaritaMc
- Look to the Evenstar
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- Joined: Wed Jan 09, 2013 10:14 pm
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by MargaritaMc » Tue Apr 08, 2014 6:13 pm
Thanks a lot - I missed that Apod. Life was a bit fraught in January. I'll read through it and see what I can make of it. Whatever it is, this new paper by Timothee Delubac et al seems to confirm the first findings. Whatever they mean!
All I can make out is that it confirms that the curvature of the universe
is flat...
Indeed the BAO imprint in cross-correlation was strong. Delubac and his team combined their autocorrelation results with the cross-correlation results of Font-Ribera and his team, and they converged on narrow constraints for the BAO scale. Autocorrelation and cross-correlation also converged in the precision of their measures of the universe’s expansion rate, called the Hubble parameter. At redshift 2.34, the combined measure was equivalent to 68 plus or minus 1.5 kilometers per second per million light years.
“It’s the most precise measurement of the Hubble parameter at any redshift, even better than the measurement we have from the local universe at redshift zero,” says Font-Ribera. “These results allow us to study the geometry of the universe when it was only a fourth its current age. Combined with other cosmological experiments, we can learn about dark energy and put tight constraints on the curvature of the universe – it’s very flat!”
But I'm mystified about the pressure waves being (like? actually?) sound waves.
M
"In those rare moments of total quiet with a dark sky, I again feel the awe that struck me as a child. The feeling is utterly overwhelming as my mind races out across the stars. I feel peaceful and serene."
— Dr Debra M. Elmegreen, Fellow of the AAAS
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MargaritaMc
- Look to the Evenstar
- Posts: 1836
- Joined: Wed Jan 09, 2013 10:14 pm
- Location: 28°16'7"N 16°36'20"W
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by MargaritaMc » Wed Apr 09, 2014 9:45 am
In the OP, I said that I was puzzled by reference to sound waves. Geckzilla pointed me to the Apod discussion in January and in that there was a link to Mark Whittle's most helpful
site,
Big Bang Acoustics: Sounds From The Newborn Universe
which resolved my bemusement.
http://www.astro.virginia.edu/~dmw8f/BB ... unit4.html
Sound in Space!?!
As school children we learn that the roar of interstellar space-craft or the zing of photon torpedoes are fictions of the movies – we know that outside our atmosphere the vacuum of space must be utterly silent. So how can sound be present in the Universe? Surely this contradicts one of our earliest learned "facts" of science? The answer is that space was not always so empty...
The previous sections remind us that at the time of Cosmic Sound the Universe was much smaller (by at least a factor of 1000), and all the matter we now find in stars and galaxies was spread out uniformly. Add to this the fact that the young Universe was also much hotter, and we learn that over the first million years, all of space was filled with a hot thin uniform glowing gas, a billion times denser than the current cosmic density. Not only did the Universe have an atmosphere – in a sense, it was an atmosphere. It was within this atmosphere that sound waves could form and move in the young Universe.
Margarita
"In those rare moments of total quiet with a dark sky, I again feel the awe that struck me as a child. The feeling is utterly overwhelming as my mind races out across the stars. I feel peaceful and serene."
— Dr Debra M. Elmegreen, Fellow of the AAAS
