Team Shines Cosmic Light on Missing Ordinary Matter

Jan 07, 2010

(PhysOrg.com) -- An international team of scientists, led by University of Maryland astronomer Stacy McGaugh, has found that individual galactic objects have less ordinary matter, relative to dark matter, than does the Universe as a whole.

Just published in the Astrophysics Journal (e-version), these results were presented by McGaugh today during a press conference at the American Astronomical Society Meeting in Washington, D.C.

Scientists believe that all ordinary matter, the protons & neutrons that make up people, planets, stars and all that we can see, are a mere fraction -- some 17 percent -- of the total matter in the Universe. The protons and neutrons of ordinary matter are referred to as baryons in particle physics and cosmology.

The remaining 83 percent apparently is the mysterious "," the existence of which is inferred largely from its gravitational pull on visible matter. Dark matter, explains McGaugh "is presumed to be some new form of non-baryonic particle - the stuff scientists hope the Large Hadron Collider in CERN will create in high energy collisions between protons."

McGaugh and his colleagues posed the question of whether the "universal" ratio of baryonic matter to dark matter holds on the scales of individual structures like galaxies.

"One would expect galaxies and clusters of galaxies to be made of the same stuff as the universe as a whole, so if you make an accounting of the normal matter in each object, and its total mass, you ought to get the same 17 percent fraction," he says. "However, our work shows that individual objects have less ordinary matter, relative to dark matter, than you would expect from the cosmic mix; sometimes a lot less!"

Just how much less depends systematically on scale, according to the researchers. The smaller an object the further its ratio of ordinary matter to dark matter is from the cosmic mix. McGaugh says their work indicates that the largest bound structures, rich clusters of galaxies, have 14 percent of ordinary baryonic matter, close to expected 17 percent.

"As we looked at smaller objects - individual galaxies and satellite galaxies, the normal matter content gets steadily less," he says. "By the time we reach the smallest dwarf satellite galaxies, the content of normal matter is only ~1percent of what it should be. (Such galaxies' baryon content is ~0.2percent instead of 17percent). The variation of the baryon content is very systematic with scale. The smaller the galaxy, the smaller is its ratio of normal matter to dark matter. Put another way, the smallest are very dark matter dominated.

"This raises an obvious question," McGaugh says, "where are all these missing baryons? The short answer is, we don't know. There are various lines of speculation, most of which are either easily dismissed or are un-testable. So for now this is a problem without an obvious solution."

Explore further: Witnessing the early growth of a giant

More information: "The Baryon Content of Cosmic Structures," Astrophysics Journal, Stacy S. McGaugh, James M. Schombert, W.J.G. de Blok, Matthew J. Zagursky

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NeilFarbstein
Jan 07, 2010
This comment has been removed by a moderator.
RobertKarlStonjek
5 / 5 (1) Jan 07, 2010
In the paper in 'Figure 1' they show that galaxy clusters fall close to a line representing the cosmic fraction fb=0.17. Galaxies, whether dominated by gas or stars, fall below the line, more so for ever smaller galaxies.

Any theory explaining this phenomena must also explain how galaxy clusters are made up of a much smaller proportion of dark matter than the galaxies which constitute those clusters. How can a cluster of galaxies contain more baryonic matter than the galaxies that constitute it??

Impossible!!!
PPihkala
3.7 / 5 (3) Jan 07, 2010
Recent news was that magnetic fields are at least 10x larger than generally assumed at galaxies. I wonder how all this magnetic attraction affects those calculations.
Rohitasch
not rated yet Jan 08, 2010
In the paper in 'Figure 1' they show that galaxy clusters fall close to a line representing the cosmic fraction fb=0.17. Galaxies, whether dominated by gas or stars, fall below the line, more so for ever smaller galaxies.
Any theory explaining this phenomena must also explain how galaxy clusters are made up of a much smaller proportion of dark matter than the galaxies which constitute those clusters. How can a cluster of galaxies contain more baryonic matter than the galaxies that constitute it??

Impossible!!!


Wow! It seems like the total is greater than the sum of its parts!!!! Deja vu, thermodynamics!
Pointedly
5 / 5 (1) Jan 08, 2010
Perhaps there are no "missing baryons." Perhaps there are other reasons for our measuring differences in baryon/dark matter ratios. I do not dispute the general accuracy of the measured differences. However, the differences do nothing to prove there are any baryons missing. If there are no missing baryons, then we have that much more to discover about dark matter, itself.
abhishekbt
not rated yet Jan 08, 2010
Must be exciting work this though. The scientists working on this must get the feeling that they are on the verge of a breakthrough!

Like reaching out to grab something which is just beyond reach, something 'dark'!
danman5000
not rated yet Jan 08, 2010
"Team sheds light on missing ordinary matter," but when asked where the ordinary matter is they reply with "we don't know." Nice.
Caliban
1 / 5 (1) Jan 08, 2010
Another question- does each galaxy in a cluster have its own dark matter "halo", or is the Halo in position encircling the cluster?
Perhaps the interaction between dark and ordinary matter "thins" the ordinary matter at the outer edges of the space occupied by the cluster- somehow driving it towards the core of the space, and thereby increasing its density further in?
Nik_2213
not rated yet Jan 08, 2010
So tidal encounters between dwarf and large galaxies which turn the former into 'Newtonian' globular clusters must strip their dark matter as well as their clouds of gas, dust etc etc ??

Interesting...

Would the data and distances exclude MOND ? I suspect not, for authors would have said...
rwinners
not rated yet Jan 10, 2010
What is the barionic content of the earth?

About that answer, I ask "how do we know?"
jsa09
not rated yet Jan 10, 2010
Seems that there could even be a fundamental error with dark matter theory. Since we are making measurements based on .... what?

What exactly are we measuring to come up with these answers?

I suspect it is orbital velocity but I don't know. If it is orbital velocity or apparent momentum then we should consider applying other explanations to the results to see if anything fits.

Having looked at MOND I cannot see how it can work. I have checked several different ways it does not make sense. However, given that the galaxies have a magnetic/electric field then we can a better understanding of the reason for orbital velocity within a field.
yyz
not rated yet Jan 22, 2010
RKS,

Remember to take into account baryonic matter in the intracluster medium. Galaxy clusters are found to have between 10-50% of the total stellar mass residing in the ICM. This recent review of "Diffuse Light in Galaxy Clusters" elaborates: http://arxiv1.lib...23v1.pdf