Map of distribution of galaxies.  Credit: M. Blanton and the SDSS.

Dark Matter is Missing From Cosmic Voids

17 Aug , 2008 by

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Cosmic voids really are devoid of matter. Astronomers have found that even the pervasive ‘dark matter’ which accounts for about 80% of the mass of the universe is not present in these voids, which are areas of vast emptiness in space that can be tens of millions of light-years across. “Astronomers have wondered for a quarter-century whether these voids were ‘too big’ or ‘too empty’ to be explained by gravity alone,” said University of Chicago researcher Jeremy Tinker, who led the new study using data from the Sloan Digital Sky Survey II (SDSS-II). “Our analysis shows that the voids in these surveys are exactly as big and as empty as predicted by the ‘standard’ theory of the universe.”

The largest 3-dimensional maps of the universe show that galaxies lie in filamentary superclusters interlaced by cosmic voids that contain few or no bright galaxies. Researchers using SDSS-II and the
Two-Degree Field Galaxy Redshift Survey (2dFGRS) have concluded that these voids are also missing the “halos” of invisible dark matter that bright galaxies reside in.

A central element of the standard cosmological theory is cold dark matter, which exerts gravity but does not emit light. Dark matter is smoothly distributed in the early universe, but over time gravity pulls it into filaments and clumps and empties out the spaces between them. Galaxies form when hydrogen and helium gas falls into collapsed dark matter clumps, referred to as “halos,” where it can form luminous stars.

But astronomers were not sure if the areas that are devoid of galaxies were also devoid of dark matter, or if the dark matter was there, but for some reason stars just didn’t form in these voids.
The research team used bright galaxies to trace the structure of dark matter and compared it with computer simulations to predict the number and sizes of voids.
Princeton University graduate student Charlie Conroy measured the sizes of voids in the SDSS-II maps. “When we used galaxies brighter than the Milky Way to trace structure, the biggest empty voids we found were about 75 million light years across,” said Conroy. “And the predictions from the simulations were bang-on.”

The sizes of voids are ultimately set, Conroy explained, by the small variations in the primordial distribution of dark matter, and by the amount of time that gravity has had to grow these small variationsinto large structures.

The agreement between the simulations and the measurements holds for both red (old) and blue (new) galaxies, said Tinker. “Halos of a given mass seem to form similar galaxies, both in numbers of stars and in the ages of those stars, regardless of where the halos live.”

Tinker presented his findings today at an international symposium in Chicago, titled “The Sloan Digital Sky Survey: Asteroids to Cosmology.” A paper detailing the analysis will appear in the September 1 edition of The Astrophysical Journal, with the title “Void Statistics in Large Galaxy Redshift Surveys: Does Halo Occupation of Field Galaxies Depend on Environment?”

News Source: SDSS and The Ohio State University


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Jon Hanford
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Jon Hanford
August 17, 2008 2:42 PM
Great article Nancy, thanks for including the name of the forthcoming paper, as I’ll be looking for an e-print of it. This story dovetails with the earlier one on star streams found around our galaxy (I know, there from the same symposium). Smaller accreting galaxies are thought to be Dark Matter dominated(both now & in the early universe) and eventually end up forming the larger galaxies we see near us today (hence the stellar streams detected by SDSS & other observations). Also, a very, very small number of galaxies have been positively detected in some voids. How they got there is now being debated, but much more research is needed to answer this question. Looking forward for any… Read more »
erichansa
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erichansa
August 18, 2008 3:54 AM

i once knew a hooker named cosmic void.

agmartin
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agmartin
August 17, 2008 9:59 PM

If dark matter is not distributed evenly maybe the dark energy isn’t either. I wonder if there is a a way to determine how dark energy is distributed.

Dave Nofmeister
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Dave Nofmeister
August 18, 2008 7:09 AM

I’m afraid I don’t understand JamesB rant, myself.

JamesB
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JamesB
August 18, 2008 1:39 AM
I’m certainly glad that my source of income and living expenses does not depend on cosmology. This gives me the freedom to explore alternative theories, even ones that diverge greatly from the mainstream. I’m not forced to either acknowledge ideas as ‘dark matter’ or ‘dark energy’ or lose my paycheck! But if I did, THIS is the kind of thing I would most likely come up with!! I can plant any interpretation on the data I wanted too and there is NO WAY anyone can say it’s wrong because ‘dark stuff’ is taken as an article of faith in cosmology!! It’s a win-win situation for me and whatever organization I represented, which means more money and my mortgage… Read more »
Dutch Delight
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Dutch Delight
August 18, 2008 2:06 AM

JamesB, your rant is awkwardly late, and misinformed at that.

“I’m not forced to either acknowledge ideas as ‘dark matter’ or ‘dark energy’ or lose my paycheck!”

Wow… I’m left wondering if you understand what science and research is actually about.

LLDIAZ
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LLDIAZ
August 18, 2008 9:37 AM

I thought gamma ray bursts come from every direction in the sky?
How can this be if there is supposedly nothing with in a void to cause the burst.

LLDIAZ
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LLDIAZ
August 18, 2008 9:41 AM

I see the need for simulations but I dont trust them. There are too many variables in reality to try and fit it nicely with in a computer. Maybe if you had a quantum computer…

JamesB
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JamesB
August 18, 2008 3:30 AM
Dutch – good for you! But have you ever wondered what would happen if the dogma of the day was discredited? Look up ‘aether’ and the Michelson/Morley Experiment (1887) if you aren’t familiar with it. For years they thought that ‘aether’ HAD to exist as the ONLY explanation of how light propagated thru space (they thought light waves were kinetic, like sound waves). For years and years the ‘aether’ theory dominated and then Michelson & Morley created an experiment to answer the prevailing question of the time “Did the Earth move thru the aether, or did it drag the aether along with it?”. The result of the experiment was the only result they had never anticipated. Null. Nada.… Read more »
JamesB
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JamesB
August 18, 2008 3:47 AM

Dutch – ” awkwardly late”?

Please explain!

Jon Hanford
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Jon Hanford
August 18, 2008 4:25 AM

JamesB, “awkardly late” as in Fritz Zwicky’s 1933 observations of galaxy motions in the Coma Cluster. He realized that there’s not enough visible matter in this cluster to hold it together, hence his idea, now widely accepted, of ‘dark matter’. Gotta agree w-Dutch on this one, your notion of ‘fictitious’ Dark Matter is 75 years late.

David R.
Member
David R.
August 18, 2008 6:14 AM
JamesB… @”I’m certainly glad that my source of income and living expenses does not depend on cosmology. This gives me the freedom to explore alternative theories, even ones that diverge greatly from the mainstream.” I don’t understand this comment. Are you saying that you ignore the discipline of cosmology in order to undertake the freedom of exploring alternative theories? @”I can plant any interpretation on the data I wanted too and there is NO WAY anyone can say it’s wrong because ‘dark stuff’ is taken as an article of faith in cosmology!!” I don’t understand this comment, either. Even the mainstream “celebrity” personalities in the field do not ascribe faith to their position–it’s a hypothesis yet to be… Read more »
neoguru
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neoguru
August 18, 2008 6:52 AM

A good article, but there are many “ifs” involved. It would have been better to report “Dark Matter THOUGHT to be Missing From Cosmic Voids”. A small detail, but the headline is somewhat misleading, infering it to be a factual conclusion rather than the result of a computer simulation.

Andy
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Andy
August 18, 2008 7:32 AM
I wonder what Newton’s Second Law would look like if he had used galactic rotation as a starting point when he formulated it. And what would we be doing now when we discovered that there were problems when attempts were made to scale it down to “local” levels? Perhaps positing the existence of Light Matter? It just seems out of place to try to explain DM as some type of really exotic matter and then expect us to believe that, in spite of the oddities, it still obeys the same law of gravity. Are we sure that the gravitational constant is the same for DM? What if it isn’t? Are we positive that it obeys the inverse square… Read more »
Astrofreak
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Astrofreak
August 18, 2008 7:37 AM

Oh please, stop it with all these “simulations” stories…. Seems you guys know everything about dark whatever, except of course what it is, where it came from, why it exists, a complete picture of what it does, whether or not it exists indefinitely or decays/increases, what its “made” of, and on and on…

Ignoramus
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Ignoramus
August 18, 2008 9:10 AM

When you simulate what you want to see, you end up seeing what you simulate.

Warren Platts
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Warren Platts
August 18, 2008 9:26 AM

It seems to me that the conclusion of the simulation is that it’s not the case that there are massive amounts of dark matter in the void spaces separating galaxy clusters. So the paper could be taken as evidence against the existence of exotic dark matter.

As for the first positing of dark matter, that would actually be the positing of a hidden planet to explain orbital irregularities of Uranus.

Jon Hanford
Member
Jon Hanford
August 18, 2008 9:31 AM
I can think of several ‘simulation’ scenarios that paid off in a big way for astrophysicists. Detailed mathematical studies of the Big Bang theory predicted the existence of the Cosmological Microwave Background radiation decades before its existence was verified (because of the lack of instruments to detect it). Black holes were predicted again through rigorous mathematical studies (simulations) long before astronomers actually unambiguously detected them. Current simulations are now frequently done on computers, but these simulations use detailed mathematical models & as few assumptions as possible to try to flesh out thorny astrophysical issues. Should the astronomical community just ignore all theoretical ‘simulations’ because they seem whimsical to non-astronomers. My point is that computer models & serious mathematical… Read more »
Demerit
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Demerit
August 18, 2008 9:44 AM

Before microscopes, people used to blame diseases on “bad humours” or evil spirits.

Cut the scientists some slack. Geez.

Chuck Lam
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Chuck Lam
August 18, 2008 8:23 PM

Why couldn’t dark matter be evidence suggesting primordial dark energy slowly morphing into hydrogen and eventually into all that we see in any direction. Morphing energy might explain cosmic chaos. Maybe the “big bang” wasn’t so big. The microwave background could be a signature. Universal expansion might be no more complicated then like-polarity repulsion. Maybe gravity flips after a certain scale. And just maybe we can’t see the trees for the forest.

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