Biggest galactic map will throw light on 'dark energy'

July 14, 2016
A slice through the map of the large-scale structure of the Universe from the Sloan Digital Sky Survey and its Baryon Oscillation Spectroscopic Survey. Each dot in this picture indicates the position of a galaxy six billion years into the past. The image covers about 1/20th of the sky, a slice of the Universe 6 billion light-years wide, 4.5 billion light-years high, and 500 million light-years thick. Color indicates distance from Earth, ranging from yellow on the near side of the slice to purple on the far side. Credit: Daniel Eisenstein and SDSS-III.

An international team of astronomers has created the largest ever three-dimensional map of distant galaxies in a bid to help them understand one of the most mysterious forces in the universe.

Scientists including a team led by Dr Florian Beutler at the University of Portsmouth's Institute of Cosmology and Gravitation have spent a decade collecting measurements of 1.2 million as part of the Sloan Digital Sky Survey III (SDSS-III).

This will allow them to make the most precise measurements to date of '' – the force that is driving the accelerated expansion of the universe.

Dr Beutler said: "This extremely detailed three-dimensional map represents a colossal amount of work. The University of Portsmouth has worked with partner institutions for ten years, helping to gather measurements of galaxies making up a quarter of the sky.

"Using this map we will now be able to make the most accurate possible measurements of dark energy, and the part it plays in the expansion of the universe."

The new measurements were carried out by the Baryon Oscillation Spectroscopic Survey (BOSS) program of SDSS-III.

Shaped by a continuous tug-of-war between dark matter and dark energy, the map revealed by BOSS allows astronomers to measure the of the universe and thus determine the amount of matter and dark energy that make up the present-day universe.

A collection of papers describing these results was submitted this week to the Monthly Notices of the Royal Astronomical Society.

BOSS measures the expansion rate of the Universe by determining the size of the baryonic acoustic oscillations (BAO) in the three-dimensional distribution of galaxies.

The original BAO size is determined by pressure waves that travelled through the young universe up to when it was only 400,000 years old (the Universe is presently 13.8 billion years old), at which point they became frozen in the matter distribution of the Universe.

Measuring the distribution of galaxies since that time allows astronomers to measure how dark matter and dark energy have competed to govern the rate of expansion of the Universe.

To measure the size of these ancient giant waves to such sharp precision, BOSS had to make an unprecedented and ambitious galaxy map, many times larger than previous surveys.

At the time the BOSS program was planned, dark energy had been previously determined to significantly influence the expansion of the Universe starting about 5 billion years ago. BOSS was thus designed to measure the BAO feature from before this point (7 billion years ago) out to near the present day (2 billion years ago).

The Sloan Digital Sky Survey and its Baryon Oscillation Spectroscopic Survey has transformed a two-dimensional image of the sky (left panel) into a three-dimensional map spanning distances of billions of light years, shown here from two perspectives (middle and right panels). This map includes 120,000 galaxies over 10% of the survey area. The brighter regions correspond to the regions of the Universe with more galaxies and therefore more dark matter. Credit: Jeremy Tinker and SDSS-III

Dr Beutler said: "If dark energy has been driving the expansion of the Universe over that time, our maps tells us that it is evolving very slowly, if at all. The change is at most 20 per cent over the past seven billion years."

Dr Rita Tojeiro, of the University of St Andrews, a partner in the project, added: "We see a dramatic connection between the sound wave imprints seen in the 400,000 years after the Big Bang to the clustering of galaxies 7-12 billion years later.

"The ability to observe a single well-modelled physical effect from recombination until today is a great boon for cosmology."

The map also reveals the distinctive signature of the coherent movement of galaxies toward regions of the with more matter, due to the attractive force of gravity. Crucially, the observed amount of infall is explained well by the predictions of general relativity. This agreement supports the idea that the acceleration of the expansion rate is driven by a phenomenon at the largest cosmic scales, such as dark energy, rather than a breakdown of gravitational theory.

Dr Jeremy Tinker, of New York University, added: "BOSS has marked an important cosmological milestone, combining precise clustering measurements of an enormous volume with extensive observations of the primary cosmic microwave background to produce a firm platform for the search for extensions to the standard cosmological model.

"We look forward to seeing this programme extended with the coming decade of large spectroscopic surveys."

Explore further: Astronomers release the largest ever 3-D map of the sky

More information: Publications:

1. Jan Niklas Grieb, Ariel G. Sánchez, Salvador Salazar-Albornoz et al. (the BOSS collaboration) The clustering of galaxies in the completed SDSS-III Baryon Oscillation, Spectroscopic Survey: Cosmological implications of the Fourier space wedges of the final sample, submitted to MNRAS, arxiv.org/abs/1607.03143

2. Salvador Salazar-Albornoz, Ariel G. Sanchez, Jan Niklas Grieb et al. The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: Angular clustering tomography and its cosmological implications, submitted to MNRAS, arxiv.org/abs/1607.03144

3. Ariel G. Sanchez, Jan Niklas Grieb, Salvador Salazar-Albornoz et al. The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: combining correlated Gaussian posterior distributions, submitted to MNRAS, arxiv.org/abs/1607.03146

4. Ariel G. Sanchez, Roman Scoccimarro, Martin Crocce et al. The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: cosmological implications of the configuration-space clustering wedges, submitted to MNRAS, arxiv.org/abs/1607.03147
Source

5. Florian Beutler, Hee-Jong Seo, Shun Saito et al. The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: Anisotropic galaxy clustering The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: Baryon Acoustic Oscillations in Fourier-space, submitted to MNRAS, arxiv.org/abs/1607.03150

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14 comments

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kminotaur32
4.6 / 5 (10) Jul 14, 2016
Awesome! Thanks for the data, and pics!
gculpex
1.5 / 5 (6) Jul 14, 2016
Would be more interesting if the locations were based on where they are now rather than where they were.
Da Schneib
4.3 / 5 (11) Jul 14, 2016
Great stuff! We've all been waiting for results from BOSS for a long time. Now we see the connections between the BAOs, the CMB, and the evolving distribution of galaxies. I expect the paper will be cited a lot.
OdinsAcolyte
4.4 / 5 (9) Jul 14, 2016
Congratulations! Awe inspiring and, whew, what a ton of work.
Mind boggling and the scale is inconceivable. I SEE it but to know these dots are galaxies....wow.
And 13 billion years (when you say it) demeans the duration involved. And earth is a quarter this age. An old world with still so much yet to come. And it is nowhere near forever. It would make even a god tire. A born mortal could never bear it. Wow.
Again, congratulations. This is sincerely humbling.
OdinsAcolyte
4.3 / 5 (6) Jul 14, 2016
Congratulations! Awe inspiring and, whew, what a ton of work.
Mind boggling and the scale is inconceivable. I SEE it but to know these dots are galaxies....wow.
And 13 billion years (when you say it) demeans the duration involved. And earth is a quarter this age. An old world with still so much yet to come. And it is nowhere near forever. It would make even a god tire. A born mortal could never bear it. Wow.
Again, congratulations. This is sincerely humbling.
big_hairy_jimbo
3.5 / 5 (4) Jul 14, 2016
WOW, love that the data suggests there ISN'T a breakdown of gravitational theory. That's a BIG RESULT.
torbjorn_b_g_larsson
4.2 / 5 (5) Jul 15, 2016
Notably these observations confirm the latest Planck data. Especially it gets an identical result on the Hubble parameter (H0 = 67.6 + 0.7 −0.6 vs 67.8 +/- 0.9 km/s/Mpc; http://xxx.lanl.g...02.01589 ), interesting now that Riess et al has published supernova data that is just shy of a 3 sigma tension here. The galaxy and supernova data, which should rely on the same distance ladder eventually, should suffer from much the same systematic errors.

But the main difference in my eyes is that our image of the universe naively grows another factor 1000 larger since the last observation. Their curvature term implies the universe can have a radius at least 3,300 times the observable universe's, or 4*10^10 times the volume that we can see. (Can have, the uncertainty is not any better than Planck's.)

Space, space, everywhere.
viko_mx
1.6 / 5 (7) Jul 16, 2016
Dark energy sound like a classical Babilonian misticism.

Its make an impresion to the more observable people how modern metaphysicians are trying to explain the physical reality in which we are living with the invisible and elusive for tha scientific equipment fictional phenomena like darn matter and energy, black holes, qunatum fluctuaations, hidden dimensions, ets...,which are not consistent wihth the scientific principles but rely wholy on the highly speculative philosophical thinking. From this disease suffer modern fundamental physics put at the service of the golden calf and dedicated to denying the Creator and Supporter of the universe and life in it because of His will and law, which are love to Him and the neighbor.
gculpex
not rated yet Jul 17, 2016
Dark energy sound like a classical Babilonian misticism.

Its make an impresion to the more observable people how modern metaphysicians are trying to explain the physical reality in which we are living with the invisible and elusive for tha scientific equipment fictional phenomena like darn matter and energy, black holes, qunatum fluctuaations, hidden dimensions, ets...,which are not consistent wihth the scientific principles but rely wholy on the highly speculative philosophical thinking. From this disease suffer modern fundamental physics put at the service of the golden calf and dedicated to denying the Creator and Supporter of the universe and life in it because of His will and law, which are love to Him and the neighbor.


And your main point is...?
Da Schneib
1 / 5 (1) Jul 17, 2016
Would be more interesting if the locations were based on where they are now rather than where they were.
You can work that out from the known changing rate of expansion and their observed redshifts. But you always start with the observed data, which can only show where they were, not where they are, because the speed of light is finite and maximal.
nikola_milovic_378
Jul 18, 2016
This comment has been removed by a moderator.
nikola_milovic_378
Jul 18, 2016
This comment has been removed by a moderator.
nikola_milovic_378
Jul 18, 2016
This comment has been removed by a moderator.
antialias_physorg
3.7 / 5 (3) Jul 18, 2016
Would be more interesting if the locations were based on where they are now rather than where they were.

The issue of 'now' is a very iffy one on cosmological scales. If you were to plot the state of th universe based a 'now' relative to Earth time then that wouldn't tell you much.
Remember that information interchange is limited to speed of light
In our everyday experiences information interchange is, for all intents and purposes, instantaneous to a good approximation. This does not hold at large distances.

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