Clash of Clusters Separates Dark Matter From Ordinary Matter

by Nancy Atkinson on August 27, 2008

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Credit: X-ray(NASA/CXC/Stanford/S.Allen); Optical/Lensing(NASA/STScI/UC Santa Barbara/M.Bradac)

Credit: X-ray(NASA/CXC/Stanford/S.Allen); Optical/Lensing(NASA/STScI/UC Santa Barbara/M.Bradac)

A powerful collision of galaxy clusters captured by NASA’s Hubble Space Telescope and Chandra X-ray Observatory provides evidence for dark matter and insight into its properties. Observations of the cluster known as MACS J0025.4-1222 indicate that a titanic collision has separated dark matter from ordinary matter. The images also provide an independent confirmation of a similar effect detected previously in a region called the Bullet Cluster. Like the Bullet Cluster, this newly studied cluster shows a clear separation between dark and ordinary matter.

MACS J0025 formed after an enormously energetic collision between two large clusters. Using visible-light images from Hubble, the team was able to infer the distribution of the total mass — dark and ordinary matter. Hubble was used to map the dark matter (colored in blue) using a technique known as gravitational lensing. The Chandra data enabled the astronomers to accurately map the position of the ordinary matter, mostly in the form of hot gas, which glows brightly in X-rays (pink).

As the two clusters that formed MACS J0025 (each almost a whopping quadrillion times the mass of the Sun) merged at speeds of millions of miles per hour, the hot gas in the two clusters collided and slowed down, but the dark matter passed right through the smashup. The separation between the material shown in pink and blue therefore provides observational evidence for dark matter and supports the view that dark-matter particles interact with each other only very weakly or not at all, apart from the pull of gravity.

On the Chandra website, there are two animations, one that shows the different views of this cluster viewed by the different observatories, and another depicting how the galaxies may have collided.

Bullet Cluster.  Credit:  NASA/CXC/CfA/STScI

Bullet Cluster. Credit: NASA/CXC/CfA/STScI

These new results show that the Bullet Cluster is not an anomalous case and helps answers questions about how dark matter interacts with itself.

Sources: HubbleSite, Chandra

About 

Nancy Atkinson is Universe Today's Senior Editor. She also is the host of the NASA Lunar Science Institute podcast and works with Astronomy Cast. Nancy is also a NASA/JPL Solar System Ambassador.

Thomas August 28, 2008 at 5:39 AM

I agree w/a previous post here. If DM exists, why is it we only seem to see it waaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaay far away, but have no particle here to say, “this is DM”? Again, DM is just a placeholder in the math under we better understand the underlying math that makes the universe tick.

Essel August 28, 2008 at 5:56 AM

Very poor, confusing and irrelevant wordings used in the article.

“As the two clusters that formed MACS J0025 (each almost a whopping quadrillion times the mass of the Sun) merged at speeds of millions of miles per hour, the hot gas in the two clusters collided and slowed down, but the dark matter passed right through the smashup. The separation between the material shown in pink and blue therefore provides observational evidence for dark matter and supports the view that dark-matter particles interact with each other only very weakly or not at all, apart from the pull of gravity.”

When two galaxy clusters are colliding, the observational evidence is their relative red-shift. Merger of the two galaxy clusters even at Millions of miler per hour would take millions of years to complete and we may not have observed them for more than a few years. We have therefore not observed them enough to quote “but the dark matter passed right through the smashup”. Most probably the observational inputs from Hubble and Chandra were fed into supercomputers for simulation of the smash-up and what came out of the simulation has been theorized here.

Without any basis the conclusion looks so foolish. The two clusters of blue material are widely separated by some hundreds of millions of light years then how is one theorizing that they are “not interacting with each other”? The only way dark matter is indirectly detected are due to gravitational interactions and therefore what else can you detect other than “pull of gravity”, when the two DM clusters are millions of years away from smashing through?

Kyle August 28, 2008 at 7:30 AM

@ Thomas:
DM has also been inferred in the motion of the Milkey Way’s globular clusters and the rotation speed of other “local” galaxies.

Jon Hanford August 28, 2008 at 8:31 AM

Nancy, thanks again for the insightful article on a further piece of evidence in favor of DM. Despite many clueless or misguided posts above, its’ nice to see some thoughtful, intelligent comment on the true scientific meaning of this latest discovery. Astute, scientifically accurate responses to the DM debate give me hope that a few astronomically savvy readers frequent UT, now one of my most popular astro-sites. Keep up the good work. Scientifically interested readers should check out the 10 page paper on this system at ArXiv:0808.2320v2 at the arXiv astro-ph site, of follow links to the paper available at some of the press release sites. Again, a remarkable piece of observational astronomy, cograts to all involved in this study.

phasespace August 28, 2008 at 10:20 AM

Thomas,

The math has already been checked. In fact, these observations actually disproves mathematical modifications to gravitational theory (like MOND). MOND necessarily predicts that there can be no separation between the “dark matter” and the normal matter because they are one and the same. However, the separation between the lensiing distribution and the visible gas makes it clear that MOND (and other math based modifications) can not be right.

robbb August 28, 2008 at 10:23 AM

i think there is a way to disagree with aspects of DM & DE articles without insulting the writers, who do a fine job and stimulate further debate and discussion.

i may be stating the obvious, but we seem to be at an impasse in our understanding of the nature of the universe. the huge leap forward by Einstein hasn’t been matched by a contemporary thinker. which points towards E’s brilliance and also the increasing complexity we seem to keep discovering around us.

technological advances seem to be adding greater mysteries. which, in a way, is as it should be. if everything were obvious what would we be left to ponder?

Matt August 28, 2008 at 11:17 AM

Bridh Hancock wrote: “I would like to see this photo again, but with annotation saying what is happinging to what, where and how. Please spell it out more clearly for me. I would like to know where the DarkMatter is. Is the DM truly invisible? and what has it done and where?
I wonder if that information will help others and the comments will improve.”
The pink part of the picture is where the visible matter is, the blue part is where the dark matter is. The fact that dark matter is on both sides of the collision, where no visible matter is shows us that, while the visible matter was slowed down by the collision, the dark matter simply passed through.

Yes, dark matter is invisible in so far that it doesn’t give off light. The way we know that something must be there is because matter warps space-time. If we see that the background galaxies beside both clusters are distorted even though we don’t see anything there it shows us that there is invisible mass.

Thomas August 28, 2008 at 11:30 AM

Kyle and Phasespace:

I don’t doubt that something is happening which looks like there should be more matter there when in fact we cannot find it, but to put some sort of place holder (DM) to make the math work means either one of two things:

1) There is dark matter, and we need to get started on finding such a thing here to prove it or

2) The math we are using to calculate these things is flawed, and DM is a “place holder” or variable we add to the original math to make it fit.

Well, we can’t seem to isolate “DM” in laboratories here, and it doesn’t fit into the standard model well without creation of other unprovable particles and dimensions. Occum’s razor easily makes quick work of this. The original math is probably flawed.

Skeptic Tim August 28, 2008 at 12:11 PM

Hi Nancy: Thanks for a well written article about MACS J0025.4-122. The evidence presented in this paper, taken along with the evidence from the Bullet Cluster may be interpreted, convincingly, that the dark matter components of these clusters behave like collisionless systems. This is, of course, not the only possible interpretation of this evidence. Presumably, a similar analysis of this system to that done by J. R. Brownstein and J.W. Moffat in arXiv:astro-ph/0702146v3 13 Sep 2007 “The Bullet Cluster 1E0657-558 evidence shows Modified Gravity in the absence of Dark Matter” where they were able to model the Bullet Cluster system without non-baryonic dark matter, could also be performed for this system; it would be interesting to see such a comparison!
However, as Z.K. Silagadze has pointed out in arXiv:0808.2595v2 [astro-ph] 20 Aug 2008 “Mirror dark matter discovered?” Dark matters behaviour in the Abell 520 cluster indicates a significant self-interaction cross-section,k not a collisionless gas. It is hard for the WIMP based dark matter models to reconcile such a diverse behaviour.
Interestingly, dark matter is usually mapped using gravitational lensing of background objects under the assumption that the dark matter provides the necessary mass; a very reasonable hypothesis. But R.H. Sanders and D.D. Land, arXiv:0803.0468v2 [astro-ph] 22 Apr 2008 “MOND and the Lensing Fundamental Plane: No need for dark matter on galaxy scales” have shown that, at least in the cases of the 36 strong gravitational lenses studied by Bolton et al. (2007) the “…observed projected mass within one-half an effective radius is consistent with the mass in visible stars plus a small additional component of “phantom dark matter” resulting from the MOND contribution to photon deflection.” It would seem to be possible that dark matter may not be necessary to account for the observed lensing effects.
Moreover, dark matter is often invoked to explain the behaviour of galaxy rotation curves – indeed, if my memory serves me correctly, apparently anomalous rotation curves of galaxies gave rise to the dark matter concept – but, again, there are other explanations as well: see, for example, David Tsiklauri’s paper arXiv:0806.1513v1 [astro-ph] 9 Jun 2008 “Galaxy rotation curves without non-baryonic dark matter and modifications to gravity: effect of the Ampere force”, or Dilip G. Banhatti’s presentation For IAU Symposium 254 on Galaxy Disk in Cosmological Context “Newtonian mechanics & gravity fully model disk galaxy rotation curves without dark matter” (Sorry, I’ve lost the arXiv reference, however the author has provided his email addresses: dilip.g.banhatti@gmail.com, banhatti@uni-muenster.de within the manuscript so I suppose he is willing to forward his work to the interested reader.
In light of the DAMA results that suggest an anomalous signal apparently modulated by earths orbit, dark matter in some form (the mirror matter hypothesis looks interesting) may be proven to be a necessary postulate; until it is so proven, we should remain open to other possibilities.

RetardedFishFrog August 28, 2008 at 6:04 PM

Yeah…
what he said.

Jarod August 28, 2008 at 8:19 PM

hahaha good one retardedfishfrog!

Mike August 28, 2008 at 8:43 PM

“I agree w/a previous post here. If DM exists, why is it we only seem to see it waaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaay far away, but have no particle here to say, “this is DM”?”

Someone correct me if I’m wrong, but the only way we are aware of dark matter is from its gravational effects on other matter. It doesn’t interact with light (or any form of EM AFAIK). Remembering that gravity is by far the weakest of your forces, we’ll only be able to detect DM when massive ammount of it interact with massive ammounts of “real” matter, or do something to visible light, like gravatiation lensing…etc…

Rob D August 28, 2008 at 10:38 PM

@Mike:
Right. Since we’re dealing with effects that can only be felt on astronomical scales, we have to get pretty damn far away to be able to pick them up clearly. It’s like saying “If this cup and this spoon both exert a gravitational force on one another, why aren’t they flying together all the time?” Build a planet-sized cup and a planet-sized spoon and leave them within a few thousand km of each other, and you’ll see gravitational effects. It’s a question of the scale on which the effect is observable.

dennis cottle August 29, 2008 at 3:52 AM

I still think the term dark matter has caused a lot of problems. Unknow Gravitational Affector (UGA) would be a term that could stop a lot of bad science and start the astro. community working together to try and work out whats going on out there and here.

Matt August 29, 2008 at 5:45 AM

dennis cottel: “Unknow Gravitational Affector (UGA) would be a term that could stop a lot of bad science and start the astro. community working together to try and work out whats going on out there and here.”

I would like to know what this “bad science” is you’re talking about and what you suggest should be done differently. How do you think would the treatment of the scientific community change by giving the phenomena a different name? I’m genuinely interested.

Jon Hanford August 29, 2008 at 8:04 AM

Thanks to Skeptic Tim for the refs to alternate explanations of the observations made in these (possibly) DM dominated galaxy clusters. I’ve seen the MOND alternative paper on the ‘Bullet Cluster’ & the ‘mirror DM’ papers, but the others are new to me, so thanks again. I’ve also read papers at the arXiv.org site refuting MOND & TeVeS gravity models of the ‘Bullet Cluster’ (alas, I don’t have the reference papers at hand), but I do note that the paper I mentioned above claimed that MOND theory did not match observations on MACS J0025, 1E 0657-56 or CL 0024+17. While I try to keep an open mind on these possible alternatives to conventional gravity models, I think more work needs to be done to possibly firm up & bolster these alternatives, by way of predictions or fitting of data to their models exclusively. Anyway, thanks for some relevant refs on these alternatives, great food for thought.

Amir Mohammad August 31, 2008 at 12:19 AM

“… another depicting how the galaxies may have collided.
I saw the second movie. I think the above title is wrong.
the true title is: “… depiciting how the clusters may have collided.”
Amir
Tehran
Iran

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