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Dark Matter Exists
olclops writes "It's a big day for astrophysics. After much speculation, scientists now have conclusive proof of dark matter. This result doesn't rule out alternate gravity theories like MOND, but it does mean those theories will have to account for exotic forms of dark matter."
The announcement of the pending announcement regarding Dark Matter
I guess he's never heard of Zaphod Beeblebrox.
"A universe that's dominated by dark stuff seems preposterous, so we wanted to test whether there were any basic flaws in our thinking," said Doug Clowe of the University of Arizona at Tucson, and leader of the study. "These results are direct proof that dark matter exists."
Also a bit of info on physorg
How does the Coalsack Nebula fit into this? It's dark and it's matter, right?
A feeling of having made the same mistake before: Deja Foobar
...the server must have known of the impending slashdot effect and preemptively protected it's CPU from the impending meltdown
A black hole is where God divided by 0
How does this effect the Stargate program?
bluespaceradio.com - New Wave, Indie and Alternative
Here's some info from NASA.
Post-rock/Ambient/Drone and other noise.
It's a big day for astrophysics.
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I think it's going to be a big day for their webmasters as well.
Now it's our turn to hide from the dark matter and wait for it to discover us! Come one everyone - pick a hiding spot and get to it! Hurry!
Hexy - a strategy game for iPhone/iPod Touch
It may be spread uniformly in the intergallactic space, meaning it's useless with density under a gram per cubic kilometer. Or it may form denser formations at distances that are useless. I mean, we're harnessing power of only one star out of a whole universe of them...
Anagram("United States of America") == "Dine out, taste a Mac, fries"
Funny, I always figured the announcement of experimental confirmation of dark matter would first be published in a scientific journal or announced at a news conference...not on a blog shared by Mark, Claire, and Sean, whoever they may be.
* Note that I tried to go back and confirm the names and finish reading the story so I would have something intelligent to say, but apparently the user's CPU allottment only accounts for 20% of the server's total, suggesting that there may be another form of CPU cycles that don't interact with visitor's to the linked site. I think we should call these "dark CPU cycles."
The full paper can be found here. From the abstract:
We present new weak lensing observations of 1E0657558 (z = 0:296), a unique cluster merger, that enable a direct detection of dark matter, independent of assumptions regarding the nature of the gravitational force law. Due to the collision of two clusters, the dissipationless stellar component and the fluid-like X-ray emitting plasma are spatially segregated. By using both wide-field ground based images and HST/ACS images of the cluster cores, we create gravitational lensing maps which show that the gravitational potential does not trace the plasma distribution, the dominant baryonic mass component, but rather approximately traces the distribution of galaxies. An 8 sigma significance spatial offset of the center of the total mass from the center of the baryonic mass peaks cannot be explained with an alteration of the gravitational force law, and thus proves that the majority of the matter in the system is unseen.
does this mean grey matter exists as well?
http://chandra.harvard.edu/photo/2006/1e0657/
For those who prefer here are the salient links which TF"A" (it's a blog entry) is referencing: http://chandra.harvard.edu/chronicle/0306/devil/ http://chandra.harvard.edu/press/06_releases/press _082106.html
Caveat Utilitor
To draw any conclusions about the potential applications of this material is pretty much impossible until we actually work out what it is.
After much speculation, scientists now have conclusive proof of dark matter.
Well, their proof is based on the detection of gravity and gravitational fields. Every real American knows that it's not "gravity", but "intelligent falling". Gravity is a myth invented by foreign scientists to make all Americans seem overweight.
The theory of relativity doesn't work right in Arkansas.
Astronomers observed a distant cluster of galaxies in optical light, with ordinary telescopes, and in X-ray light, with a telescope in space. This is an unusual cluster of galaxies, since there is clear evidence that one small group of galaxies are "interlopers:" members of a smaller cluster which fell into a larger one some time ago. Members of this interloping group are all bunched together at one side of the main cluster.
The visible light image shows the galaxies within the cluster. It also shows, much fainter and much smaller, a very large number of BACKGROUND galaxies -- these are objects way, way farther away than the big cluster. As the light from these background galaxies passes through the big cluster, it is bent very slightly by the gravitational field of the cluster. This gravitational lensing distorts the shapes of the faint, little background galaxies just a bit, but with care, we can measure the effect. We learn from the lensing where the matter is in the cluster: that is, we can figure out where the stuff which produces gravitational effects is distributed. That's part one: a map of the matter within the cluster, based on gravitional lensing.
The X-ray image shows emission from hot gas within the cluster. We have known for several decades now that large clusters of galaxies are immersed in giant clouds of very hot gas, at temperatures of millions of degrees. The gas emits copious amounts of X-rays. In most clusters, the amount of this hot gas -- its total mass -- is much larger than the amount of mass we can see in stars. That is, counting the stars in the galaxies suggests a total amount of mass-in-stars M, but computing the amount of hot gas necessary to emit all the observed X-rays yields a mass-in-hot-gas of around 10*M, ten times as much.
On the other hand, the amount of mass derived from the gravitational lensing of background galaxies is about 10 times larger still, or about 100*M. The stuff which produces the gravitational lensing does not emit visible light, nor X-ray light, nor, as far as we can tell, any electromagnetic radiation. Therefore, we call it "dark matter". It produces a gravitational force, but that's about all we know about it. (There are additional reasons for believing that this mysterious stuff is not made up of electrons, protons and neutrons, but that's another story).
This new result is interesting for this reason: the X-rays appear on one region of the cluster of galaxies, telling us that the bulk of the ordinary matter is RIGHT HERE. The map of total mass we can make from gravitational lensing appears in a different region of the cluster, telling us that the bulk of the dark matter is OVER THERE. It is very clear that the dark matter and ordinary matter are distributed in different places. This isn't too surprising, perhaps, if one small group of galaxies rammed into a big cluster -- the gas ram pressure might push on the ordinary hot gas in a different way than on the dark matter (which wouldn't feel any ram pressure at all, actually).
As Martin Hardcastle pointed out to me in a Google newsgroup a few days ago (thanks, Martin!), this is certainly not the first evidence for dark matter -- we have a number of examples in which gravitational forces are larger than the amount of visible matter would suggest -- but it is the first good case in which the distribution of the dark and ordinary matters are so clearly displaced.
Michael Richmond "This is the heart that broke my finger."
mwrsps@rit.edu http://stupendous.rit.edu
...just supposition. After reading all this, all I see is that dark matter, which cannot be observed by any means other than gravitational effects on other non-dark-matter matter and seems suspiciously absent from everyday experience and experiment here on Earth, must exist because we think we see mass and energy behaving in a way that goes with our theories, yet we've seen it behave that way before and it is only in recent times we've decided that something is wrong with physics and we need dark matter.
Can anyone say aether? I knew you'd try...
We have next to zero understanding of the quantum vacuum, and don't know for certain if everything should pop in and out there including not only electrons and photons, but antiprotons and neutral pi mesons and everything else too. We do know it exists from many many Earth-side experiments and reams of dead trees covered in equations. We don't know how the potential fields exist which give rise to the fields we know, we don't know how any of them link in all ways to the nuclear fields which we also don't understand too well but we have loads of equations and experiments for those.
So we invent something, call it "dark matter", and look for anything we can then say matches our thought experiments and we can forgo all the careful Earth-side experiments. We just sort of treat the absence of any dark matter here or anywhere near here as one of those Hitchhiker's Guide SEPs.
More science-by-supposition and proof-by-spectacle. Show me the proof. Show me why dark matter has to exist. Prove it out with careful calculation and application to everything across the board. We've set off fifty megaton nukes for crying out loud without a single sign of anything amiss that would suggest we have a giant hole in physics requiring dark matter. We've done experiments on electromagnetic fundamentals, nuclear forces, and so on and along the way, we didn't hear of a need to invent dark matter.
But some people look at the cosmos and decide that despite not truly understanding the whole picture of physics at every scale yet, we can claim that dark matter exists and here's proof. Where in the Nine Hells does this stuff fit with the physics theories they alread promulgate as accepted science to be taught in universities?
It looks like modern aether, and it looks as though anyone buying it will be upset when someone working right along on the regular investigations into quantum physics and spacetime and so on puts it together and says, "oh, here's why that galaxy moves that way. We didn't need dark matter after all..."
If my grammar and spelling are off, I am [distracted/tired/careless] (take your pick)
I say we use it to build a dyson sphere around the entire universe. Then we can finally solve the question of whether the universe is expanding / contracting / balancing. The hard way.
I had read that if the universe were infinite that the sky would be blindingly white from all the old light from old stars, which is one of the reasons that a Big Bang (or other creation) was assumed to have happened.
But if there are dark clouds that can absorb the light, could there be stars further than 13ish billion light years away, that are simply obscured?
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I haven't yet read this article due to it being slashdotted, but I'm sure it is at least as credible as the story about the new source of free energy from magnets and as accurate as the one that says goldfish are smarter than dolphins.
1 voice in a sea of voices
Bring a heavy ship! Remember: each pound of weighs over 10,000 pounds.
Proof by very large bribes. QED.
Storm
We know nothing, and yet you can post bitchy comments to slashdot, on a computer, connected to the Internet, powered by a physical plant hundreds or thousands of miles away piping electricity directly into your laptop, and then watch a show on TV over cable distributed by satellite.
I'd hazard a guess that we actually do know a thing or two.
Anyone who loves or hates any language, platform, or manufacturer, doesn't know what they're talking about.
that the night sky is not the temp of the suns surface is called olbers paradox http://jersey.uoregon.edu/~imamura/123/lecture-5/o lbers.html.
I believe the resoluiton of this paradox is one of hte outstanding successes of the expanding universe idea discoverd by hubble
George Bush hates dark matter
This data provides no evidence for the makeup of the dark matter.
Other observations suggest that the dark matter is not Massive Compact (Halo) Objects, or MACHOs. The idea that dark matter might be composed of some sort of Weaking Interacting Massive Particle, or WIMP, is a bit out of fashion these days, but still a possibility, as far as I know.
Michael Richmond "This is the heart that broke my finger."
mwrsps@rit.edu http://stupendous.rit.edu
From the title - "This result doesn't rule out alternate gravity theories like MOND". Actually, this directly rules out MOND. That's a big part of the point of the experiment.The idea is that the mass in these clusters doesn't come from the obvious sources of visible matter (the gas), as it would in a MOND or normal gravity scenario, but rather from the invisible (i.e., dark) matter.
Clearly, this matter which refuses to reflect light in our visible spectrum has something to hide. Ergo, it is terrorism and must be quashed.
Consciousness is a myth. Trust me.
Remember Vulcan, the planet with an orbit inside of Mercury? It was PROVEN to exist in the late 1800s. The calculations showed that Mercury's orbit required a smaller planet to make Mercury's orbit precess as it did. People even went looking for it with the finest telescopes of the day. And they saw it.
Then some smart aleck who worked in a patent office came along and showed that space is warped and that Mercury's orbit fits perfectly. Vulcan disappeared, never to be seen again.
Vulcan had more data in favor of its existence back then than dark matter does now. Pardon me, but I'm as skeptical as parent.
There is an infinite amount of knowledge (when we learn new things, we are presented with new questions), but only a finite amount of things that we can know. Of course our knowledge is incomplete. It always will be.
That does not mean we shouldn't try to learn as much as possible, however. What we have accomplished is far beyond what any other animal on earth has done.
From the NASA press release: "These results are being published in an upcoming issue of The Astrophysical Journal Letters."
Two points. First, journals really hate it when press releases are made prior to the publication date. Second, this journal has an "impact factor" of ~5-6, compared to Nature, or Science, which have impact factors of ~25. Why are they publishing in some obscure journal if this is really the rock-solid proof that they claim it is?? Makes me wonder.
"we know nothing"
A mistake known as "generalising from self"; you know nothing, therefore you assume that everybody else must know nothing too (not your fault, you cannot conceive of anything else). This is a primitive form of reasoning called "induction", whilst it can have its place, it often leads to huge inaccuracies such as deriving "we know nothing" from "I know nothing".
Proof of your limited ability to use logic:
"we know nothing, and what we do know..."
The two are mutually exclusive; we cannot both know nothing, and have stuff that we do know.
Proof of your lack of knowledge:
"Science-is-infallible types claim to know and understand the universe"
No they don't. They claim to be trying.
With both a lack of knowledge and a lack of ability to use logic, one might think the two would cancel out and you'd get a thing or two right, but I guess you're pretty unlucky, which would explain the bitterness too.
The revolution will not be televised... but it will have a page on Wikipedia
A steaming pile of Dark Matter was found on the sidewalk and traced back to Nibbler's litterbox. Bad Nibbler!
It must have been something you assimilated. . . .
Did anyone else notice the amazing quality of TFA? I actually understand more about dark matter from that article than from anything else I have read on the subject to date. This makes me less grumpy about all the money I felt was "wasted" on telescopes vs. planetary exploration.
Quidquid latine dictum sit, altum viditur.
This appears to be no more a confirmation for dark matter than when the Michelson-Morley experiment (in 1881) "confirmed" the existence of ether. In the immediate aftermath of the Michelson-Morley experiment, theoreticians generated lots of mathematical "proofs" (e.g., The Ether of Space, Sir Oliver Lodge, Harper & Bros, 1909) that showed how a boundary layer in the ether surrounding the Earth accounted for the observed results. A series of subsequent refinements of the Michelson-Morley experiment showed that the speed of light was truly independent of direction, and Einstein's theories, which did not require the existence of ether, provided a better fit for the observed results than was a boundary layer in the ether.
Over time, the Michelson-Morley experiment was recognized to have disproved the existence of ether -- but it wasn't that way initially.
Alternative explanations include "quantum critical phase transitions", and I'm sure that there are other possibilities, that a series of observations of similar cosmological events will provide the range of data needed to select the hypothesis that best describes the observations.
Being able to fudge one theory to fit a single observation falls quite a bit short of a "conclusive proof". Maybe dark matter does exist, but it's going to take a lot more observations for it to be convincing to me.
How precisely does dark matter permit the expansion of the universe to be defined, and how precisely does the observed phenomenon fit those numbers?
Wake me up when someone has a quantum mechanical model that tells how quarks are bound together in dark matter, or when someone manages to tap into dark energy (which is supposedly all around us).
The last time I checked, emperical observation provided confirmation of theories, not proof. Proofs are what you get in mathematics.
Sean at 11:52 am, August 21st, 2006
The great accomplishment of late-twentieth-century cosmology was putting together a complete inventory of the universe. We can tell a story that fits all the known data, in which ordinary matter (every particle ever detected in any experiment) constitutes only about 5% of the energy of the universe, with 25% being dark matter and 70% being dark energy. The challenge for early-twentyfirst-century cosmology will actually be to understand the nature of these mysterious dark components. A beautiful new result illuminating (if you will) the dark matter in galaxy cluster 1E 0657-56 is an important step in this direction. (Heres the press release, and an article in the Chandra Chronicles.)
A prerequisite to understanding the dark sector is to make sure we are on the right track. Can we be sure that we havent been fooled into believing in dark matter and dark energy? After all, we only infer their existence from detecting their gravitational fields; stronger-than-expected gravity in galaxies and clusters leads us to posit dark matter, while the acceleration of the universe (and the overall geometry of space) leads us to posit dark energy. Could it perhaps be that gravity is modified on the enormous distance scales characteristic of these phenomena? Einsteins general theory of relativity does a great job of accounting for the behavior of gravity in the Solar System and astrophysical systems like the binary pulsar, but might it be breaking down over larger distances?
A departure from general relativity on very large scales isnt what one would expect on general principles. In most physical theories that we know and love, modifications are expected to arise on small scales (higher energies), while larger scales should behave themselves. But, we have to keep an open mind in principle, its absolutely possible that gravity could be modified, and its worth taking seriously.
Furthermore, it would be really cool. Personally, I would prefer to explain cosmological dynamics using modified gravity instead of dark matter and dark energy, just because it would tell us something qualitatively different about how physics works. (And Vera Rubin agrees.) We would all love to out-Einstein Einstein by coming up with a better theory of gravity. But our job isnt to express preferences, its to suggest hypotheses and then go out and test them.
The problem is, how do you test an idea as vague as modifying general relativity? You can imagine testing specific proposals for how gravity should be modified, like Milgroms MOND, but in more general terms we might worry that any observations could be explained by some modification of gravity.
But its not quite so bad there are reasonable features that any respectable modification of general relativity ought to have. Specifically, we expect that the gravitational force should point in the direction of its source, not off at some bizarrely skewed angle. So if we imagine doing away with dark matter, we can safely predict that gravity always be pointing in the direction of the ordinary matter. Thats interesting but not immediately helpful, since its natural to expect that the ordinary matter and dark matter cluster in the same locations; even if there is dark matter, its no surprise to find the gravitational field pointing toward the visible matter as well.
What we really want is to ta
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No. We can also see things by the light they BLOCK from stars. If it was just matter, we would have seen it, and conclusively proved it's existance, long ago.
Slashdot gets worse every day... Pipedot: News for nerds, without the corporate slant
Yes, they have ruled out "non-very-well-lit regular matter." As you surmised, "dark matter" doesn't mean that no light is coming from it. Technically it refers to everything that's not baryonic matter (aka "regular" matter -- the category that includes every particle we have ever directly observed, including neutrinos).
As I understand it, the way they did it in this case is by knowing the temperature of the galaxies. If there were regular matter causing the observed gravitation, it would be hot enough to give off some sort of radiation that could be picked up via telescope. They may also have measured how much light from behind is being absorbed. In addition, if it were regular matter that interacts with other regular matter, it probably would have followed a similar pattern to the gas clouds, which means the center of gravity would have stayed with the observable clouds rather than separating like it did. (They probably have more reasons why it can't be regular matter, but that's what I could come up with off the top of my head late at night.)
My understanding is that gravitational lensing here suggests that dark matter hangs out around "cold matter" or solid matter, like stars and planets, but not "hot matter" like plasma. Why would the mysterious dark matter only stay with the solid matter? What theory of dark matter predicts that it ignores plasma? Am I missing something?
Table-ized A.I.
There are two things at work here: one, there is much more dark matter than normal matter so the normal matter is actually hanging out with the dark matter rather than the other way around and two, the dark matter is very weakly interacting; especially with the very low density X-ray plasma.
Actually I think particle physicists are happy there's all this exotic unknown matter floating out there. Most modern particle theories practically scream for there to be (as of yet undiscovered) supersymmetric partners of all known particles. If dark matter turns out to be SUSY particles that would be a great experimental confirmation. If I had to bet, that would be my guess as to what dark matter will turn out to be. The great thing about science is there's always something unexpected around the corner, it would be really boring if we knew everything already.
it reeks of PR. ... the kind of PR that happens when people are REALLY trying to get others accept a point that is hard to accept.
I've been following the "dark" story on and off since I stopped studying physics seriously after college. The MOND system makes a whole lot of sense. My non-professional-physicist read on the MOND / DARK controversy is that several of the alternate theories (like MOND) that remove the need for dark matter are fairly convincing. Dark matter is not convincing at all - not testable, not observable, and reminds me a lot of Santa Claus. Somebody brought the presents, right? The problem is that a vast majority of cosmologists are all so far down the dark matter band wagon that if dark matter goes away... lots of careers will be lost. Destroyed. These professionals who trade solely in reputation and intellectual-ism will have their rug pulled right out from under them.
A much more plausible explanation is that some people are trying really hard to amp up the PR. Sort of like what happens when you need a distraction from a big debate, so you get all the airline travelers to throw away liquids. Anyone who tells you they have proof for something that by definition can not be observed is selling PR. For those of you who believe it without question, I've got a bridge I'll sell you.
After taking about 30 minutes and reading no less than 6 heavily biased PR pieces... I say this stinks. It's certainly not science - (yet).
So what's new then? All along the whole case for "dark matter" was that galaxies -- _all_ galaxies -- rotate strangely like a rigid body, except right near the centre. According to newtonian mechanics the stars in a galaxy should behave basically like the planets in our solar system: the farther from the centre you get, the slower they move. But in a galaxy stuff moves like that only near the centre, and then it's like gravity changed gradually from 1/(R*R) to 1/R, and the stars rotate at an almost constant angular velocity around the centre.
;)
So from there it's that either:
1. there's a metric buttload of matter we can't observe other than through gravity, in some weird distribution all through the galaxy's disc, or 2
2. we accept that gravity isn't working like we think it does
(Or my favourite: 3. galaxies are just a rotating texture there, so _of_ _course_ they rotate like a rigid. Noone would be dumb enough to simulate the individual stars just to give us a pretty sky in this MMO we call RL
And somehow the favourite is 1, for no obvious reason than that noone wants to modify gravity theories. It's as if Galileo, upon discovering that a stone dropped from the mast doesn't lag behind the ship, would then proceed to invent some "dark wind" that pushes the stone along with the ship. Since existing wind obviously isn't strong enough to push the stone that hard, it's got to be some dark wind in there too. Just, you know, for the sake of not contradicting the existing Aristotelian system.
Anyway, all along we knew that it can't be conventional matter, because we already had plenty of galaxies in various states of illumination and they all behave the same.
So exactly how does the new one help there? It seems to me like it still can't offer conclusive proof that 1 is true and 2 is false, because it would _still_ be equally well explained by 2. What this "solves" is at most a sub-distinction inside 1, once we're dead-set on believing 1 instead of 2. It says basically that if we already decided it's 1, then, yep, it's definitely not baryon matter (rocks, gases, protons, etc), but some weird matter that interacts only with gravity.
A polar bear is a cartesian bear after a coordinate transform.
Take a gander at the published paper. A large part of the reason that this galaxy cluster in particular was chosen was because it is one of the cases known where we have a clear-cut idea of what's going on.
Their initial assumption (page 1 right column): "During a collision of two clusters, galaxies behave as collisionless particles, while the fluid-like X-ray emitting intracluster plasma experiences ram pressure. Therefore, in the course of a cluster collision, galaxies spatially decouple from the plasma." Since the area occupied by dense matter (stars) is more than 10^11 times smaller than that of the whole cluster, literally one or two stars might impact each other. Meanwhile, the intracluster gas is, however diffuse, GAS - it can't pass through itself, and is observed to contain ~80-90% of a cluster's visible mass.
I don't know the specifics of how this is done, but they used a gradient of the change in a background galaxy's size and related it to the curvature of space (and hence amount of mass). By plotting a lot of background galaxies, they were able to integrate the gradient to find the center of mass (warning: not 100% sure of this explanation) that was causing the lensing (green gradient lines on page 2).
When this is compared with an x-ray image of the gas which is known to comprise most of the visible mass of clusters, the two mismatch by about 6 arc seconds. On page 4, they discuss the probability of other clusters creating the apparent mass (1/10 million chance) or entire filaments of intergalactic mass creating it (1 in 100 million). The only remaining conclusion from this is that something which fits the description of dark matter (in that it has mass but no other measurable property) makes up the great majority of the cluster's mass and the two clouds of it passed through each other like the galaxies.
So, they expected the stars/dark matter and the gas of colliding clusters to separate in a collision, and this is exactly what was observed
That's a good question - this is termed the "cooling flow problem". We expect to see lots of gas cooling in relaxed clusters (not the colliding one discussed here) as the gas is dense in the central regions. However there's a lack of evidence of cool gas, so most people think something is heating it (although there are many solutions possible http://uk.arxiv.org/abs/astro-ph/0010509). The ideal candidate is the central supermassive black hole (AGN), however it is difficult to understand how this process works. One idea is that sound waves can transport the energy from the black hole into the cluster, heating it (see e.g. http://chandra.harvard.edu/press/05_releases/press _120105.html)
Errr, last I heard they were pretty sure we're open. It was on the edge for a while, but the discovery of Dark Energy (NOT the same thing as Dark Matter, btw) made the open/heat death ending a virtual certainty. They had already taken the gravitational effects of Dark Matter into account for these equasions, so this discovery (which merely shows that Dark Matter can/does exist in distinct regions away from Baryonic matter) changes nothing.