Another piece in the dark matter puzzle

October 5, 2007 By Miranda Marquit, feature
Another piece in the dark matter puzzle
The blue and red haze is the x-ray emission from the gas. The green contours represent the gravitational potential mapping the mass distribution in the cluster of galaxies. The authors looked at the the matter "blob" to the right of the yellowish gas front. This blob originally came from the left, and within some 100,000 years it moved through the larger blob to the left, where the gas was separated. Credit: Data from the Chandra x-ray telescope, courtesy of Signe Riemer-Sørensen.

Most scientists agree that most of the matter in the universe is dark. Dark matter, which is undetectable through direct observation, can only be inferred because of its effects on the matter that we can see.

“In principle,” Signe Riemer-Sørensen, a scientist at the Dark Cosmology Centre at the University of Copenhagen, tells, “dark matter can’t be seen directly. We know it has to be some kind of particle that we have not seen on earth, and that it can exist without being detected here.”

Riemer-Sørensen is one of many scientists around the world interested in studying dark matter. Because it is so prevalent, physicists agree that understanding how dark matter works is an important fundamental question that could lead to a better knowledge of the universe, and the basic laws upon which it operates. Riemer-Sørensen and her group, which also consists of scientists from the University of Patras and the Aristotle University of Thessoaloniki in Greece, and the University of Oslo, are working on a way to pin down some of the characteristics of dark matter.

“We took one specific theory about dark matter,” Riemer-Sørensen explains. “We look at a specific type of decaying particles, and if they represent dark matter, they will decay and transform into photons in x-rays.” The particles in question are axions, hypothetical elementary particles used in theories describing “extra” dimensions. The idea, she says, is to look for an area of the universe that has a great deal of dark matter, and then look for weak x-ray emissions.

Riemer-Sørensen and her peers looked at colliding clusters of galaxies. “A good place to do this is clusters of galaxies because they are very heavy and consist of approximately 85 percent of dark matter. The stars and galaxies are only about five percent, and then there is about 10 percent hot gas, which does also emit x-ray.”

She points out that the galaxies within clusters of galaxies do not collide in the classical sense. Rather, they pass through each other. “The only thing colliding is the gases in the galaxy cluster.” During the galactic collision, the gases are displaced due to friction.

“You compare this to the gravitational potential from dark matter,” Riemer-Sørensen continues. “Because the two galaxy clusters have collided, and the gas has been displaced. In a normal cluster of galaxies, the galaxies, the gas, and the dark matter are all contained within the same region. In the colliding case there is a clear separation, and to find the putative x-ray emission from axions, we look in regions where there is a lot of mass, but very little gas.”

So, did Riemer-Sørensen and her colleagues find the weak dark matter x-ray emissions? “We didn’t find any clear signs of x-ray emissions from axions in these regions,” she says. “And that tells us something about dark matter.” If dark matter particles do follow the reactions of decay set forth in the theory of axions as dark matter, then dark matter has an extraordinarily long lifetime. “If dark matter does decay,” Riemer-Sørensen insists, “then the lifetime of the axions is at least three million billion years, which is twenty thousand times longer than the lifetime of the universe.”

“This is a piece of information that tells us something about how dark matter must behave,” Riemer-Sørensen continues. “So for technical reasons x-rays can currently be eliminated as a way to detect it.”

She hasn’t stopped trying to detect dark matter more directly, however. “Now we’re working on going into gamma rays to see if there’s a signature there.”

Dark matter may have stumped scientists for three decades, but little by little the puzzle is starting to fit together.

Copyright 2007
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not rated yet Oct 05, 2007
Are the smallest contour circles a peak or valley? I assume a valleys because of the warped space time analogy?

Sounds to me like "Dark Matter" is the background of the Universe. Instead of a high mass density, it has a high energy density, and matter and dark matter exchange gravitational waves. A page of measurements of the push/pull effects between the two should explain.
1 / 5 (4) Oct 05, 2007
Smallest contours are centres of gravitational attraction commonly explained as locations of high density of dark matter but alternatively explained as locations of low density of anti-gravity matter.

1 / 5 (4) Oct 05, 2007
... and the lack of detection of x-rays is also consistent with the anti-gravity matter theory

3.7 / 5 (3) Oct 05, 2007
"Dark matter may have stumped scientists for three decades, but little by little the puzzle is starting to fit together."

Still have to directly detect ant of what's supposed to be some 90% of all matter in the universe, though.
3 / 5 (2) Oct 05, 2007
With all the conclusions about Dark Matter being so pervasive and longlived, it seems to me that Dark matter is an extreemly small particle at least smaller than the shortest wavelength of light. And like the aether of old, everywhere. But not necessarily stationary. More like the gasses filling the atmosphere, or liquids filling the seas and lakes. And I propose that light travels in waves through this sea of Dark Matter, much like waves on the ocean. Each individual wave is composed of billions of particles that themselves do not travel very far, rather just enough to transmit the energy of the light wave to the next group. Red shift would then be compared to the waves from a stone in a pond lengthening near the farthest reaches of the pond from the stone's entrance.
2 / 5 (2) Oct 05, 2007
I can't believe he (Signe Riemer-Sørensen) actually made the statement in the article:

We know it has to be some kind of particle that we have not seen on earth

He used the word - KNOW - this area of science is devoid of facts and confirmed theories. It more like conjecture on top of make it up as we go type science. I'm in the camp of their are some fundamental understandings of the universe that we just don't know yet and that's why are formulas are broken - not 90% of the universe being in hiding with a stupid name like Dark Matter. The real scientists tell the bigfoot enthusiasts to show me just one corpse - I would say to Dark Matter people - your evidence is more like blurry photos and questionable footprints - give something compelling, then make an announcement
1 / 5 (1) Oct 05, 2007
It's the "aether" as some people would have it. The universe, I hope most would agree is continuous without bounds, that, of course, we have discovered. In all reality, the only bound to our universe is our own minds. Nothing has been proved impossible forever.
3.5 / 5 (2) Oct 05, 2007
The super massive gravitational footprint of dark matter is significantly more substantial evidence than blurry pictures of Big Foot. There is no question about the existence of so-called dark matter, what it is, is a whole other question.

I'm guessing Signe Riemer-Sørensen "knows" it is a particle because it must have mass to exert gravitational influence. But what kind of particle is essential immortal? Physicist will have to think further outside the proverbial box to tackle dark matter. Perhaps, old mathematical paradigms such as particles and waves are a hindrance to grasping the nature of this thing. Maybe, we don't have the language to describe dark matter.

The implications of dark matter for the science of physics could well be revolutionary. The entire foundation of physics is now in question. Just about every astrophysical theory is now obsolete and waiting for some new insight into just what the heck is really going on here. Yet, it seems that most of the researchers involved are hoping for a more prosaic solution that will some how make a tidy fit into the bigger picture they have been painting since the 1920's.
3 / 5 (2) Oct 06, 2007
If it so long lived, it has been there for ever. It is just space time itself.
4.3 / 5 (3) Oct 06, 2007
Big Tone, I agree that 'know' was a poorly chosen word. That something exists which we havn't been able to measure is true. It's been dubbed 'dark matter' because it has not been observed. But to claim it doesn't exist is as rash as claiming to know it's properties. The universe (according to redshift) is apparently accelerating. Given the four forces, how would you explain this phenomenon without proposing another matter or energy ?
4.5 / 5 (2) Oct 15, 2007
Would it be irrational to suggest that dark matter could be a form of gravity in itself? What if dark matter was composed of gravitons? This could explain why we cannot physically detect it with current technology. It seems where there is a prevalent source of gravity, there also exists a large amount of dark matter. This hypothesis is problematic due to explaining one theoretical concept with another. I found it interesting to at least suggest it though. Any comments?

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