Simulations Predict Where We Can Find Dark Matter 61
p1234 writes with this excerpt from the Max Planck Institute for Astrophysics:
"Simulations by the Virgo team show how the Milky Way's halo grew through a series of violent collisions and mergers from millions of much smaller clumps that emerged from the Big Bang. ... If Fermi does detect the predicted emission from the Milky Way's smooth inner halo, then it may, if we are lucky, also see gamma-rays from small (and otherwise invisible) clumps of dark matter which happen to lie particularly close to the Sun. ... The largest simulation took 3.5 million processor hours to complete. Volker Springel was responsible for shepherding the calculation through the machine and said: 'At times I thought it would never finish.' Max Planck Director, Professor Simon White, remarked that 'These calculations finally allow us to see what the dark matter distribution should look like near the Sun where we might stand a chance of detecting it.'"
We discussed a related simulation a few months ago.
Re:Hope it works out for you (Score:5, Informative)
Don't bother reading the paper. They discovered that they could find dark matter "in space" if it exists.
Did you read the same article I did? Before this simulation their best guess was to look at other galaxies and target their centers. However, the simulation revealed that they have a better chance if they look at our own galaxy, but 10-30 degrees of center, where they should be able to detect gamma rays caused by dark matter.
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"Did you read the same article I did?"
this is slashdot, read the article, who has got time for that?
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....where they should be able to detect gamma rays caused by dark matter...
This assumes that dark matter generates gamma rays, a form of electromagnetic radiation. Has anybody ever scientifically demonstrated that it is possible to generate such electromagnetic radiation by means OTHER than moving electrical charges? If they do detect such gamma radiation, how will they ascertain that this radiation is NOT caused by an electrical phenomena rather than some unknown action of undiscovered dark matter?
Anytime
Re:Hope it works out for you (Score:5, Informative)
Anytime the underlying assumptions of a computer input or algorithm are faulty, even the 3 1/2 million hours of computation on a supercomputer will not lead to the discovery of the scientific truth. The principle of garbage in garbage out still applies. The bottom line is simple: the dark matter emperor is as naked as a newborn.
They have a theory about how dark matter should work. They expended 3.5M hours of computing to make a prediction based on that theory. Now they'll try to confirm the prediction empirically. If the prediction doesn't pan out, the theory will be jettisoned or patched. If the empirical observations agree with the prediction, the theory is left standing until such time as new evidence shows it to be squidgy around the edges. That's how science works.
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"Has anybody ever scientifically demonstrated that it is possible to generate such electromagnetic radiation by means OTHER than moving electrical charges?"
Yes. Go to a large hospital that has a PET scanner. They routinely generate gamma rays inside human bodies through the annihilation of positrons and electrons.
Gamma rays are generated by interactions that involve atomic nuclei or particle-particle interactions. Because of that, in most processes the gammas all have specific energies. For example, in
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...through the annihilation of positrons and electrons....
You not say that electrons or positrons are not charged and are not moving when they annihilate? What I am saying is that gamma rays are produced by electrical effects rather than gravitational interactions involving mass. Maybe I am wrong, but I was under the impression that one of the big reasons of postulating dark matter is to account for the motion of galaxies. The reason that dark matter and dark energy have not been found is really very simple
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The radiation when an electron and a positron annihilate do not come from movement, or acceleration.
I think you need to study up a bit on basic physics before you criticize the world's leading astrophysicists.
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"Moving electrical charges" and "electrical effects" suggests you're talking about Maxwell-law electrodynamics. There are many other sources of electromagnetic radiation, including atomic state transitions (e.g., fluorescence) and particle interactions (e.g., radioactive decay, particle annihilation, etc.).
Saying that electromagnetic radiation is produced by "electrical" effects is something of a tautology, as electromagnetic radiation is, as you might guess, an electromagnetic effect. However, it's well-kn
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...Saying that electromagnetic radiation is produced by "electrical" effects is something of a tautology, as electromagnetic radiation is, as you might guess, an electromagnetic effect....
Exactly, but then why is dark matter and energy postulated to exist, yet it has so far at least never been found to exist in anything other than mathematical speculations? If this postulated of dark matter produces any electromagnetic radiation, would that not of necessity mean that electrodynamic processes were involved?
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Big Assumptions (Score:3, Informative)
This assumes that dark matter generates gamma rays, a form of electromagnetic radiation. Has anybody ever scientifically demonstrated that it is possible to generate such electromagnetic radiation by means OTHER than moving electrical charges?
You are quite correct. They are making a huge assumption that dark matter can annihilate with itself. Whether it can do this depends on the type of dark matter - in some models it can in others it cannot. This is not pointless though - their work will either see it or at least put a limit on how well it does annihilate which we may be able to use to give us a better idea where to look at the LHC.
One way to avoid having charges produce photons is to have your particle partly consist of the EM field. For
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One way to avoid having charges produce photons is to have your particle partly consist of the EM field. For example, although the experiment has never been done, I think (if you are a particle theorist feel free to correct me!) you could annihilate two Z bosons to give two photons because the Z consists partly of an EM field.
I am curious as how you would make that Feynman diagram. Myself, I cannot make it work.
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Gamma is just energetic photons, more energetic than X-rays that are commercially produced by slamming electrons into tungsten targets. Gamma is typically produced by nuclear decay and is often where "missing mass" goes via the E = mC^2 so they are not an electron phenomena but a nuclear phenomena.
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...Gamma is just energetic photons...
Indeed correct, but are not all photons a manifestation of the electric interaction? In reactions involving the strong nuclear force all energy produced eventually converted to and released as electromagnetic energy. When an atomic or hydrogen bomb explodes, all sorts of exotic fragments of atoms are flying around. However, in the end all that energy created by the conversion of mass into energy is converted into and dissipated in the form of electromagnetic radiation. N
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...Gamma is just energetic photons... Indeed correct, but are not all photons a manifestation of the electric interaction?
Photons ARE the carriers of electromagnetic interaction. That does not mean, no other interaction can produce photons. You can have direct production of photons in the strong interaction too.
In reactions involving the strong nuclear force all energy produced eventually converted to and released as electromagnetic energy. When an atomic or hydrogen bomb explodes, all sorts of exotic fragments of atoms are flying around. However, in the end all that energy created by the conversion of mass into energy is converted into and dissipated in the form of electromagnetic radiation.
Again, your understanding of basic physics is lacking. Quite a bit of the energy release in a nuclear explosion is released as energetic neutrons and neutrinos.
Nowhere has the force of gravity been observed to be involved in any of this.
Who claims it has to?
Why do cosmologists have to resort to convoluted theories involving gravity and come up with undiscovered and exotic constructs such as dark matter and black holes.
1. Black holes is a consequence of relativity. Relativity has been proven to be very accurate. And, there is plenty of observational evidenc
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....Quite a bit of the energy release in a nuclear explosion is released as energetic neutrons and neutrinos....
That is true, but even then in the end these are absorbed and end up as electromagnetic energy. Neutrinos may travel quite far before this happens to them, but at some point they to will interact with with an atom somewhere and produce electromagnetic energy.
(...Black holes is a consequence of relativity...)
Not at all, in fact relativity prohibits the existence of black holes. Even a theoretical
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....Quite a bit of the energy release in a nuclear explosion is released as energetic neutrons and neutrinos....
That is true, but even then in the end these are absorbed and end up as electromagnetic energy. Neutrinos may travel quite far before this happens to them, but at some point they to will interact with with an atom somewhere and produce electromagnetic energy.
Sorry, but neutrinos do not interact electromagnetically.
(...Black holes is a consequence of relativity...)
Not at all, in fact relativity prohibits the existence of black holes.
No it does not. Go back and read up on relativity and then solve the equations. Schwarzschild did this already, however.
Even a theoretical black holes cannot be observed by definition since no light or anything else can escape them, according to the theory.
Wrong again. They still have mass and massive objects interact gravitationally. Or are you implying there is no gravity? And add to that Hawking's ideas of black hole radiation. Again, you need to read up more.
According to relativity, a black hole would have to have infinite mass.
Utterly wrong.
(...Take a look at the weak lensing results on the Bullet cluster for example....)
Quite often in science we make an observation and then try to interpret that observation. After a while, the interpretation is equated with the observation itself.
The lensing, in other words the bending of light has been INTERPRETED to be due to a massive object's gravity. We do observe that light is slightly deflected when it passes by the sun or other massive object. That is all we observe and then we speculate about its cause. In 1929 Edwin Hubble observed that starlight shifted in its spectrum toward the red. This has been known ever since as the "red shift". That is all we observe, starlight shifted to the red. This has been INTERPRETED to be caused by motion as in the familiar Doppler effect. There is evidence that the red shift is caused by the steadily increasing zero point energy of space itself.
Provide that evidence. Apparently Occam's razor means nothing to you. You say that dark matter is absurd becaus
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....Then you start talking about zero point energy in nothing more than a hand-waving fashion that is even less compelling than dark matter.....
The difference between conjectured dark matter in the distant reaches of space and the zero point energy, instead the zero point energy has been experimentally measured right here on Earth. It manifests itself in various ways, one of them is called the Casimir effect. This zero point energy, pervades all of space and affects all atomic processes.
(...when we know the
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....Then you start talking about zero point energy in nothing more than a hand-waving fashion that is even less compelling than dark matter.....
The difference between conjectured dark matter in the distant reaches of space and the zero point energy, instead the zero point energy has been experimentally measured right here on Earth. It manifests itself in various ways, one of them is called the Casimir effect. This zero point energy, pervades all of space and affects all atomic processes.
It is really sad that you don't really understand what vacuum energy is, still keep talking about in the most utterly wrong ways. Anyone who knows a little bit of quantum mechanics knows that vacuum energy is the lowest energy state of any quantum system and that this energy cannot be removed from the system. It has nothing to do with what you are conjecturing in your posts.
(...when we know the interaction is the electroweak interaction...)
This is only one facet of the electric interaction to which all leptons respond to.
Amazing, you keep talking about the "electric" interaction. Ask any particle physicist (and mind you, I am one myself), neutrinos do n
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but are not all photons a manifestation of the electric interaction?
No, photons are the carrier of the electromagnetic force so all electrical phenomina are the manifestation of the electromagnetic force, not the otherway around.
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Gamma is typically produced by nuclear decay and is often where "missing mass" goes via the E = mC^2 so they are not an electron phenomena but a nuclear phenomena.
While some gamma rays come from nuclear decay, that is far from the entire story. Most of the gamma rays we observe from space originate in particle interactions, mostly proton on proton collisions. As two protons interact, a whole slew of different particles are produced, but mainly pions. The neutral pion decays into two gammas.
On the other hand, in many astrophysical sources, blazars for example, gamma rays are produced through inverse Compton-scatterings.
Re:Hope it works out for you (Score:4, Funny)
With the way physics is goign these days, being able to determine that something is in space means you are doing pretty damn good for yourself.
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At least that narrows it down a bit? Oh...
Re:Hope it works out for you (Score:4, Interesting)
"I wonder if dark matter to them is like a Ubuntu release to most of us?"
Maybe, the answer is difficult, it's much like Schroedinger's cat.
until it's observed you cannot tell if it is there or not.
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I wonder if dark matter to them is like a Ubuntu release to most of us?
Actually it's more like fudge.
Obvious (Score:2, Funny)
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there is no such thing as dark matter.
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It's still dark matter, it's just not fuel anymore.
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If they have such a good model (Score:1, Interesting)
Instead of a gamma-ray glow map as seen from the Sun, I'd like to see 3d renderings of a whole galaxy where they artificially color dark matter to show where it is.
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Instead of a gamma-ray glow map as seen from the Sun, I'd like to see 3d renderings of a whole galaxy where they artificially color dark matter to show where it is.
I believe that was the first picture [mpa-garching.mpg.de]. Of course it was 2-D in the article, but it had to have been based off of a 3-D model. Maybe the researchers could create a Quicktime VR movie that we could spin.
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Figure 1 is the dark matter density.
But the annhiliations, assuming they happen at all, would go as density squared.
Hmmm (Score:3, Interesting)
Re:Hmmm (Score:4, Informative)
N-body simulations require a high degree of communications between processing nodes, something "@home" systems don't provide.
3.5million processor hours? (Score:2, Interesting)
my mid range processor does about 0.5GFLOPS, which means those available on the market probably range from about 0.1-2GFLOPS give or take, and then theres graphics processors, which are capable of TFLOPS these days, so there could be a factor of about 10^4 in the number of FLOP's done, i know that astrophysics often has order of magnitude calculations, but that's just a bit useless
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Processor hours are the right unit if you're trying to allocate usage of a large computer; in particular, they're the units in which compute power on large national clusters is requested in grants.
The calculation in this article was done at the LRZ in Munich, which consists of nineteen 512-core 1.6GHz Itanium systems; 3.5 million processor hours corresponds to using nine of those nineteen systems for a month.
I find (Score:4, Funny)
I find plenty of dark matter when I turn out all the lights prior to going to bed for the evening.
Specifically, I find plenty of dark matter with my toes, which doesn't result in a shout of discovery like, "Eureka!" but ,"*$&#@!"
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I for one welcome our dark matter overlord: Obama.
An obligatory cultural reference (Score:3, Funny)
LAUNCELOT: Look, my liege!
ARTHUR: Camelot!
GALAHAD: Camelot!
LAUNCELOT: Camelot!
PATSY: It's only a model.
ARTHUR: Shhh!
My little finger... (Score:1)
... also knows where it can find dark matter. And it doesn't need teraflops to do so !
places devoid of any stars (Score:4, Insightful)
Due to the proximity to the Sun, the Galactic centre is the brightest and most extended source. This makes it easier to detect than any of the small dark matter subclumps that are distributed over the sky. If one of them should also be detected, it may be devoid of any stars.
I'm interested in that last sentence. Does the gamma radiation push away hydrogen and dust, preventing the formation of stars, or does dark matter exhibit a repulsive gravitational force, clearing a region of space around it? Without referring to Wikipedia, the latter seems unlikely, but the former seems like something we should worry about. How much gamma radiation are we talking about? Should we worry about one of these clumps drifting near the solar system and sterilizing everything? (And if so, how much of an effect would these clumps have on the Drake equation?)
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I got the impression what they meant was that instead of looking at the core of a galaxy (where the dark matter is most concentrated but there are also guaranteed to be lots of stars) you stand a better chance of detecting it if you look out a little further where there are still some decent clumps but there are many fewer stars. If you get really lucky you might even find a clump that has very few stars in it.
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Don't read too much into that sentence. They're just saying that if they found a clump without stars inside it, then one can immediately rule out a star-based source of gamma radiation.
If they don't rule that out, then it will be hard to argue that the gamma rays are from dark matter, and not some other more mundane source.
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Re: 3.5 million processor hours (Score:1)
I wonder how many days 3.5 million processor hours actually is. I run SETI@home still, I wonder if that's comparable.