Comments on: Clash of Clusters Separates Dark Matter From Ordinary Matter

By: Amir Mohammad

Amir Mohammad — Sun, 31 Aug 2008 07:19:32 +0000

"… 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

By: Jon Hanford

Jon Hanford — Fri, 29 Aug 2008 15:04:47 +0000

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.

By: Matt

Matt — Fri, 29 Aug 2008 12:45:41 +0000

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.

By: dennis cottle

dennis cottle — Fri, 29 Aug 2008 10:52:02 +0000

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.

By: Rob D

Rob D — Fri, 29 Aug 2008 05:38:27 +0000

@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.

By: Mike

Mike — Fri, 29 Aug 2008 03:43:21 +0000

"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…

By: Jarod

Jarod — Fri, 29 Aug 2008 03:19:22 +0000

hahaha good one retardedfishfrog!

By: RetardedFishFrog

RetardedFishFrog — Fri, 29 Aug 2008 01:04:08 +0000

Yeah…
what he said.

By: Skeptic Tim

Skeptic Tim — Thu, 28 Aug 2008 19:11:07 +0000

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 â€œphantom dark matterâ€ 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.

By: Thomas

Thomas — Thu, 28 Aug 2008 18:30:37 +0000

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.

By: Matt

Matt — Thu, 28 Aug 2008 18:17:13 +0000

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.

By: robbb

robbb — Thu, 28 Aug 2008 17:23:56 +0000

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?

By: phasespace

phasespace — Thu, 28 Aug 2008 17:20:25 +0000

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.

By: Prime

Prime — Thu, 28 Aug 2008 15:38:11 +0000

Plasma takes many forms, both hot and cold.

Prime

By: Jon Hanford

Jon Hanford — Thu, 28 Aug 2008 15:31:15 +0000

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.

By: Kyle

Kyle — Thu, 28 Aug 2008 14:30:13 +0000

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

By: Essel

Essel — Thu, 28 Aug 2008 12:56:05 +0000

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 â€œbut the dark matter passed right through the smashupâ€. 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 â€œnot interacting with each otherâ€? The only way dark matter is indirectly detected are due to gravitational interactions and therefore what else can you detect other than â€œpull of gravityâ€, when the two DM clusters are millions of years away from smashing through?

By: Thomas

Thomas — Thu, 28 Aug 2008 12:39:34 +0000

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.

By: Aodhhan

Aodhhan — Thu, 28 Aug 2008 11:47:11 +0000

I think there is a lot of confusion when it comes to dark matter and dark energy. While there are many debates about dark energy, there really is a pretty big concensus for the existence of dark matter. The big debate is about exactly what it is or made of. Is it a force gone wild? Is it a particle we haven't seen before? blah blah. Right now, it is too small to catch; as proven by this article. It goes/passes through things and seems to linger around them afterwards in areas; in seemingly a predictable manner

The fact Another one of those crazy things we hope the LHC will help us solve.

By: sidney P. Buford

sidney P. Buford — Thu, 28 Aug 2008 11:22:21 +0000

Dark matter is real. Physical matter is dark matter transformed by dynamic energy. Even nothing is something.

By: Bridh Hancock

Bridh Hancock — Thu, 28 Aug 2008 06:58:45 +0000

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.

By: csrster

csrster — Thu, 28 Aug 2008 06:35:02 +0000

It is of course possible to buy bags of dark matter at Home Depot. The sell little else.

By: Yael Dragwyla

Yael Dragwyla — Thu, 28 Aug 2008 06:28:15 +0000

Jack Burton Says:
"i will believe in dark matter when i can go to Home Depot and buy a 10 lbs bag of it. Until then it is all crap." That's like saying "I'll believe that the Earth goes around the Sun, not vice-versa, when I can bring both into my living-room and watch what they do. Until then, it's all crap." A great many very important things that almost all of us accept as real, from gravity to the natures of the chemical elements, are only known by inference and as spinoffs of mathematical equations. Calling people names, or belittling them for accepting circumstantial evidence when it is solid *and* that's all we have for our ideas about reality, is not only stupid and uncivil, but may lead to fisticuffs. I really don't think we need to do that.

By: texzoo

texzoo — Thu, 28 Aug 2008 05:39:50 +0000

I would prefer Wal-Mart over home depot,that way, I would know it's real dark matter, because China has never made anything original.

By: robert appleton

robert appleton — Thu, 28 Aug 2008 05:18:56 +0000

I see and believe in what you are showing and sharing. Thank you.