New map of the universe reveals its history for the past six-billion years

Jan 13, 2012 By Michael Wood-Vasey
This image shows the positions of the 900,000 luminous galaxies used in four Sloan Digital Sky Survey studies described during the 2012 annual meeting of the American Astronomical Society. Each green dot represents one galaxy. The image covers a redshift range from 0.25 to 0.75, a time when the universe was between 7-billion and 11-billion years old. Credit: David Kirkby (University of California, Irvine) and the SDSS-III Collaboration

The scientists of the Sloan Digital Sky Survey (SDSS), including astronomers at Penn State, have produced a new map of the universe that is in full color, covers more than one quarter of the entire sky, and is full of so much detail that you would need five-hundred-thousand high-definition TVs to view it all. The map consists of more than one-trillion pixels measured by meticulously scanning the sky with a special-purpose telescope located in New Mexico. This week, at the annual meeting of the American Astronomical Society in Austin, Texas, the SDSS scientists announced results of four separate studies of this new map that, taken together, provide a history of the universe over the last six-billion years.

"This , constructed from observations over the past decade, is an unprecedented view of the distribution of stars, galaxies, and quasars, and allows us to trace the evolution of the constituents of the over vast swaths of cosmic time," said Donald Schneider, head of Penn State's Department of , the SDSS survey coordinator, and a coauthor on all four studies. Two additional department members, Distinguished Professor Niel Brandt and Assistant Professor Suvrath Mahadevan, are participants in the SDSS.

The final version of the SDSS map was published online last year and has been viewed more than a million times by astronomers, students, and citizen scientists from all over the world, and it has been studied in depth by international teams of scientists from the SDSS collaboration.

The scientific results announced this week are based on an investigation of the clustering of galaxies all over the sky. "The galaxies we see today give us clues to the history of our universe," says Shirley Ho, an astrophysicist at Lawrence Berkeley National Laboratory (LBL) and the Bruce and Astrid McWilliams Center for Cosmology at Carnegie Mellon University, who was the lead author of one of the papers. "The way galaxies cluster together today can tell us two things. First, galaxy clustering can provide a measuring stick to see how the universe has expanded over time. Second, we can use that information to calculate exactly how much matter the universe contains, and what fraction consists of ordinary matter, dark matter, dark energy, and neutrinos."

The other three papers explore various pieces of the universe in more detail. A team led by Hee-Jong Seo of the Berkeley Center for Cosmological Physics at LBL and the University of California Berkeley compared the observed clustering of nearby galaxies to those in the early universe to obtained a detailed picture of the universe's expansion, while a team led by Roland de Putter of the University of Barcelona used the clustering data to determine the mass of the neutrino, a subatomic particle that only recently was proven to have any mass at all. None of these results would have been possible without the work of a team led by Ashley Ross of the University of Portsmouth (UK), who carefully studied how other effects, such as the presence of stars in our galaxy, affect these conclusions.

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This movie shows the positions of the 900,000 luminous galaxies used in four Sloan Digital Sky Survey studies described during the 2012 annual meeting of the American Astronomical Society. Each green dot represents one galaxy. The image covers a redshift range from 0.25 to 0.75, a time when the universe was between 7-billion and 11-billion years old. The rotation of the image provides a view that shows what the distribution would look like from all sides. Click on the movie to start or stop playing the movie. Credit: David Kirkby (University of California, Irvine) and the SDSS-III Collaboration

The first step in the research was to identify 900,000 "luminous galaxies" seen by the SDSS -- so-called because they shine much brighter than typical galaxies, meaning that they can be seen at great distances across the universe. "By covering such a large area of sky and working at such large distances, these measurements are able to probe the clustering of galaxies on incredibly vast scales," says Martin White, a member of the research team based at Lawrence Berkeley National Laboratory and the University of California Berkeley.

The luminous galaxy measurements were used by Ross's team to determine what additional factors needed to be taken into account. "Because we are looking out at the universe from one place -- the Earth -- we don't always get a clear picture of what the universe as a whole looks like," says Ross. "We have to carefully consider what that means, to make sure that we don't mistake an accident of our Earthbound view for the true structure of the universe."

Armed with the proper estimates of how luminous galaxies cluster, the researchers compared the estimates for the clustering of nearby galaxies with those much farther away. "This analysis is one of the most trustworthy ways to measure dark energy," Seo says. "The imprint of sound waves in the early universe leaves a clear signature on the clustering of galaxies known as baryon acoustic oscillation. By comparing the size of this feature, seen in the cosmic microwave background just 300,000 years after the Big Bang, to that measured by SDSS-III for galaxies 7-11 billion years later, we can measure how the universe has expanded over that time and can learn about the nature of dark energy."

By comparing the distances to galaxies with how much the universe has expanded since light left those galaxies, astronomers can learn more about the nature of the mysterious dark energy currently driving the increasing rate of that expansion. "These studies allow us to look back six-billion years, to a time when the universe was almost half as old as it is now," said Antonio Cuesta of Yale University, a key member of all four research teams. Among the results: assuming the most widely accepted and likeliest cosmological model, the researchers found that dark energy accounts for 73 percent of the universe, with a margin of error of only two percent.

The SDSS's map covers almost unimaginably large scales but, amazingly, it also offers insights into the almost unimaginably small. The universe is full of tiny particles called neutrinos, the by-products of the nuclear reactions that make stars shine. Many trillions of the tiny particles pass harmlessly through the Earth every second. When initially discovered, it was believed that neutrinos were massless.  Recent work by particle physicists have demonstrated that the neutrino has a small mass, but they have been able to place only an upper limit on this value.

Astronomy offers another approach to determining the mass of this ubiquitous subatomic particle. A team led by Roland de Putter of the University of Valencia in Spain examined the SDSS's map to estimate the largest neutrino mass consistent with the universe we see. "One of the greatest laboratories for particle physics is the universe itself," de Putter says. The team's study pinpointed the largest possible neutrino mass at less than a millionth of the mass of an electron -- a better constraint by a factor of ten than can be offered by traditional particle-physics methods.

The four papers announced this week fit together to help in understanding the history of the universe in unprecedented detail. But even more detail is still to come. Later this year, the SDSS will publish Data Release 9, which will include highly accurate distance measurements to many galaxies, substituting these accurate measurements for the estimates used in the four new studies.

"For each and every one of our million ," Cuesta says, "we will replace its estimated distance with a very precise measure. Our upcoming map will bring the universe into sharp focus." Seeing the universe in sharp focus will almost certainly help advance our understanding of the whole universe -- from the very large to the very small.

Explore further: Violent origins of disc galaxies probed by ALMA

More information: Ross et al. (2011): "Ameliorating Systematic Uncertainties in the Angular Clustering of Galaxies: A Study using SDSS-III" 2011, MNRAS, Vol 417, pp. 1350-1373.
Ho et al. (2012): "Clustering of Sloan Digital Sky Survey III Photometric Luminous Galaxies: The Measurement, Systematics and Cosmological Implications"
Seo et al. (2012): "Acoustic scale from the angular power spectra of SDSS-III DR8 photometric LRGs"
de Putter et al. (2012): "New Neutrino Mass Bounds from Sloan Digital Sky Survey-III Data Release 8 Photometric Luminous Galaxies"

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Mayday
not rated yet Jan 13, 2012
Curious. I'm puzzled by the evenness over such a long time period and in the context of such enormous expansion. And what happened to the usual filaments-and-knots of most large scale cosmic maps? What am I missing?
Shootist
2.3 / 5 (3) Jan 13, 2012
Curious. I'm puzzled by the evenness over such a long time period and in the context of such enormous expansion. And what happened to the usual filaments-and-knots of most large scale cosmic maps? What am I missing?


Three dimensions projected onto two, combined, I think, with every pixel (galaxy) being given the same apparent brightness.
rawa1
1 / 5 (5) Jan 13, 2012
And what happened to the usual filaments-and-knots of most large scale cosmic maps?
IMO it's because these filaments are visible only when the slightest galaxies are taken into account. The Sloan Survey doesn't use very strong telescope and it's oriented to mapping of the most luminous galaxies, for which many details of dark matter structure aren't apparent. http://www.aether...tion.jpg
chardo137
3.4 / 5 (5) Jan 13, 2012
Why are the filaments and knots missing? One has to assume that it is because of the enormously greater scale of this survey. They are there, they are just so small in this image as to be almost invisible. Also they were looking at only extremely luminous galaxies to help expand the distance scale.
Mayday
not rated yet Jan 13, 2012
Thanks, everyone.
MorituriMax
5 / 5 (1) Jan 13, 2012
Okay, I'll say it... "My God! It's full of Stars!"
89118a
not rated yet Jan 15, 2012
I was hoping SDSS would find at least one billboard. :(
AntonioCuesta
5 / 5 (2) Jan 20, 2012
Hi everyone, this is Antonio Cuesta from Yale University. I did some of the research described here. To answer some of the comments above, there are a few reasons that we don't see the cosmic web very clearly in the figure. The main one is that in our study we use photometric redshifts, which are less accurate than the spectroscopic redshifts being measured during the next couple of years by SDSS-III/BOSS. Photometric redshifts are a way of estimating the distance to a galaxy if we dont have a spectrum of it. The estimate comes from machine learning using the observed colors of galaxies at known redshifts as a training set, the algorithm estimates redshifts of galaxies based only on their observed colors. Since the redshifts shown in the figure are photometric redshifts, there is a lot of uncertainty that spreads out any structure in the figure.
AntonioCuesta
5 / 5 (2) Jan 20, 2012
The other reason, of course, is the size of the figure. Even with accurate redshifts, the universe is really homogeneous at this scale. The radius of the sphere shown in the figure is 2700 Megaparsecs (8800 million light years), so even if we could see all the matter distribution - all the matter, not just the big luminous galaxies that trace this distribution - it would be very homogeneous, and it would be very difficult to see any structure unless you zoom way in.

This is just an example of the impressive volume of the universe probed by SDSS-III/BOSS!
Callippo
1 / 5 (6) Jan 21, 2012
The main one is that in our study we use photometric redshifts
This still doesn't explain, why the existing 2D illustrations of SLOAN survey results exhibit such a density structures - while the green sphere above not. http://summitlake...rvey.jpg Apparently, the above results presented are faked useless BS, which has nothing to do with observed reality.
yyz
5 / 5 (1) Jan 21, 2012
"This still doesn't explain, why the existing 2D illustrations of SLOAN survey results exhibit such a density structures - while the green sphere above not. http://summitlake...rvey.jpg Apparently, the above results presented are faked useless BS, which has nothing to do with observed reality."

Sure it does. The map you linked to is from an older 2003 survey, uses more accurate spectroscopic redshift data, and extends to only 2 Gly: http://www.newsci...rgy.html

As Antonio noted above, the present survey uses less accurate photometric redshifts and extends to much larger distances (8.8 Gly). Again, this is why this cosmic structure is not as apparent, for the exact reasons Antonio discussed.

Zephir, why not get your facts straight before you attempt to slander published work (using older, irrelevant data) about which you haven't a clue.
Gawad
5 / 5 (1) Jan 30, 2012
This still doesn't explain, why the existing 2D illustrations of SLOAN survey results exhibit such a density structures - while the green sphere above not. http://summitlake...rvey.jpg Apparently, the above results presented are faked useless BS, which has nothing to do with observed reality.


Holf F**K that was painful to READ. Wow. Just Wow. Will there ever be an opportunity to embarrass yourself and make an ass of yourself that you will actually decided to pass on? Ever?

Mr. Cuesta bothers to sign up to this site to answer some good, pertinant questions from curious interested members about this excellent work and you return the favour by ACCUSING HIM AND HIS TEAM OF SCIENTIFIC FRAUD?!?

Putting all of your history on this site into perspective and...no it's just unbelievable! Jesus Christ man, you are such a COMPLETE ASSHOLE and usless waste of skin. How, HOW do you keep from killing youself from one day to the next?
Callippo
1 / 5 (4) Jan 30, 2012
you return the favour by ACCUSING HIM AND HIS TEAM OF SCIENTIFIC FRAUD?
Nope, rather from the waste of public resources - do you have some problem with it? Apparently the distribution presented lack all details, so it's useless. The scientists need a public feedback ALL THE TIME. They're payed from the public money, not vice versa.
Gawad
5 / 5 (3) Jan 30, 2012
you return the favour by ACCUSING HIM AND HIS TEAM OF SCIENTIFIC FRAUD?
Nope, rather from the waste of public resources

You lying sack of sh*t: you WROTE "the above results presented are FAKED useless BS" THAT'S AN ACCUSTATION OF SCIENTIFIC FRAUD. F-A-K-E-D. Are you also too STUPID to understand that? Of course you are, but that hardly changes the severity of the offense. The very idea that practicing members of the scientific community could actually constructively interact with membres of the public in an open forum is one of the DREAMS OF THE INTERNET. Oh, but not for *JIGGA* or whatever your sorry assed name really is. OH NO, you have to skulk around here waiting to poison and destroy any opportunity for this that comes around.

For what it's worth, I reported your comment as abuse. I can't even image worse abuse on such a forum. I can't. Not that Physorg seems to give a rats ass about such things anymore.
Callippo
1 / 5 (2) Feb 02, 2012
THAT'S AN ACCUSTATION OF SCIENTIFIC FRAUD. F-A-K-E-D
Of course, we have better results already. This is how the density fluctuations of SLOAN survey appears: http://discoverma...nmap.jpg Why these intriguing results were replaced with homogeneous sphere? Because postdoc responsible for it was lazy enough?
Gawad
5 / 5 (1) Feb 02, 2012
THAT'S AN ACCUSTATION OF SCIENTIFIC FRAUD. F-A-K-E-D
Of course, we have better results already. This is how the density fluctuations of SLOAN survey appears: http://discoverma...nmap.jpg Why these intriguing results were replaced with homogeneous sphere? Because postdoc responsible for it was lazy enough?

No, this has been explained to you TWICE already, but like any other stupid fixated moron, you just DISMISSED THE EXPLANATIONS OUT OF HAND (see, I TOLD YOU it wouldn't be long) without any indication that you've made the slightest effort to understand anything, or providing any explanation as to why the reasons given to you might be flawed.

Instead, you just repeat your own flawed inital claim (not even an argument) that has already been pointed out to you as being bullshit.

You're the one who is pathetically LAZY, hypocrite.
Callippo
1 / 5 (3) Feb 02, 2012
My question was, why these scientifically useless results were published, if they don't reveal any details? It's like the publishing picture of flat sphere instead of map of Moon with craters. It's simply ridiculous waste of effort and money. Apparently someone needed the publication fast - so he fabricated it.
Gawad
not rated yet Feb 03, 2012
My question was, why these scientifically useless results were published, if they don't reveal any details? It's like the publishing picture of flat sphere instead of map of Moon with craters. It's simply ridiculous waste of effort and money. Apparently someone needed the publication fast - so he fabricated it.

O.k., I give up. I might as well let you in on the truth. I know Antonio is going to be really pissed of at me for this but I think this has gone far enough. I'll deal with him later, but for now, and for your sake I think you have to know what's what. Oh man.

Look, they did it because they knew it would piss you off. I know, I know, it sounds ridiculous, but we know you're hot on the trail of something huge, but we can't afford to have you DAWT guys blow appart the whole Standard Model paradigm. There's too much at stake. This is just one of many distractions. OTOH, it's ALL fake. Heck even Wood-Vasey and Physorg are in on it, so no public money was spent!
rawa1
1 / 5 (2) Feb 03, 2012
but we can't afford to have you DAWT guys blow appart the whole Standard Model paradigm. There's too much at stake..
OK, let's sing with me..

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