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Hubble and the VLT Uncover Evidence For Self-Interacting Dark Matter
astroengine writes: A new study carried out by the ESO's Very Large Telescope and the NASA/ESA Hubble Space Telescope has revealed for the first time that dark matter may well interact with itself — a discovery that, at first glance, seems to contradict what we thought we knew about the nature of this invisible mass. "In this study, the researchers observed the four colliding galaxies and found that one dark matter clump appeared to be lagging behind the galaxy it surrounds. The dark matter is currently 5000 light-years (50 000 million million kilometers) behind the galaxy — it would take NASA’s Voyager spacecraft 90 million years to travel that far. A lag between dark matter and its associated galaxy is predicted during collisions if dark matter interacts with itself, even very slightly, through forces other than gravity. Dark matter has never before been observed interacting in any way other than through the force of gravity."
Shed some light on this so called Dark Matter?
There's no evidence it isn't caused by magic particles evading galactic police forces.
Sorry everyone, I missed the million after the 90...
Is there a way to edit/delete my own posts?
Thank you, Bradley Manning, Edward Snowden and so many others, for courageously defending humanity, my freedom and more!
In a rush to tailor the evidence to a flawed theory, dark mentor was invented by humon minds in an attempt to save a beloved theory. We need to cast off the shackles of what we want to be true, and look at the evidence in a cold, anyalytical light. When this is done, I'm quite certain that there will be no need for the magical fairy dust matter that is there but isn't there.
The more examples of dark matter being found to be located away from or in a different distribution than from known matter, the more difficult it is to attribute to just gravity taking on a different form. Observations like this have already been the biggest difficulty for theories like MOND and TeVeS, to the point I've seen proponents of those theories throw up their hands when giving talks wondering if the alternative gravity theories could ever account for such phenomena, or if it should be a death knell. But their work continues just in case.
It's a good thing nobody is suggesting magic (except you).
Then wouldn't the dark matter clouds just collapse in on themselves and form singularities as there would be no counterforce to gravitational attraction?
"Because we are not employing at entry level, offshoring will kill our industry stone dead."
Bullet Cluster.
Its...The Nothing!
Yeah, because both those operate at the same time scales...
Mostly random stuff.
Yes, but if it's a question of belief (and it always is until the evidence arrives, if it ever does) my little finger tells me our understanding of gravity is just plain wrong. I read similar things sometimes from theorists who argue dark matter may not exist. It's interesting. I love contrarians. I wish the scientific establishment would nurture them more.
The dark matter is currently 5000 light-years (50 000 million million kilometers) behind the galaxy —
it would take NASA’s Voyager spacecraft 90 million years to travel that far.
Right. Would it? Okay. How is that supposed to help me imagine 5000 light years? I already know it's a bloody long way. You might as well have told me it was the length of x football pitches or y times the length of the Amazon river.
A comparison with the diameter of the galaxy in question would have been more useful.
systemd is Roko's Basilisk.
I realize the term Dark Matter is something of a placeholder for the cause of some as-yet unexplained observations but many people (including physicists) are taking the term quite literally There are three possibilities for what it could possibly be.
1) There is some form of exotic matter (or other phenomena) whose properties have yet to be discovered but which has a gravitational effect
2) There is an error in the measurements of the matter we can see
3) There is an error in the models we are using to describe the matter we can see
What I don't understand is why so many scientists are favoring 1 when 2 and/or 3 seem to be just as likely. 1 is the most exciting possibility but we have nothing more than indirect evidence for it. I'm waiting for someone to explain why so many seem so sure that it actually is some form of exotic matter. We've been down this road before. We couldn't explain phenomena like the orbit of Mercury until Einstein showed that Newtonian mechanics was merely an approximation of the more accurate relativistic models. People were trying to use the observations as evidence that there might be some undiscovered matter when really it was an inaccurate model. We also make measurement errors all the time. I just don't get how we've ruled out a measurement error or a modeling error.
"So where it takes light 5000 years to travel a distance, the Voyager would take only 90 years
That means Voyager speed is: 5000 / 90 * lightspeed = warp 55.5!"
In the Original Star Trek, "warp Factor" is cubed to give the equivalent in light speed. Thus the original 1701 Enterprise could travel 64 times lightspeed at Warp 4
By the time we get to Voyager (and presumably TNG as well) Warp 10 seems to be nearly infinite speed, and they could have got home from the Delta Quadrant fairly quickly if the could achieve Warp 10. Tom Parris and B'Elanna Torres were working on using the Delta flyer to fly ahead of Voyager to lessen the shockwave or something like that.
Oh and of coure reconfigure the main deflector to emit a reverse tachyon pulse etc
Contrary to the summary, this is one of the expected properties of Dark Matter. The leading candidate that answers the dark matter observation problem (which is already well-described by buchner.johannes above) is a new kind of particle, known as a WIMP, for Weakly Interacting Massive Particle. "Weakly" doesn't just mean "not strongly", it means "through the weak force". It's postulated that this new kind of particle, predicted by various extensions to the Standard Model of particle physics, interacts with itself through the weak nuclear force.
What we don't know very well is how efficiently this interaction takes place. Ways to measure this (and hence detect WIMP dark matter) include:
1) Direct detection: Wait for a stray WIMP to hit a block of stuff and detect a flash/vibration/decay product/whatever. Many experiments. Status: ongoing.
2) Production: Make some WIMPs in a particle collider. Status: check with LHC in a few months.
3) Indirect: The weak nuclear interaction produces some by-products, like neutrinos and gamma rays. Thus if you look at a spot where there ought to be lots of dark matter (like the center of the galaxy), you might see some extra gamma rays. The Fermi-LAT satellite is doing exactly this. Status: ongoing.
4) Behavior: The interaction will "slow down" the movement of WIMPs by introducing a little bit of drag. This would be a much much weaker version of what happens to normal matter when clouds of gas run into each other. Using gravitational lensing we can probe the mass distribution and look for such drag effects. That's what this article is addressing.
Whoever is the first to confirm the existence of dark matter (whether WIMP or otherwise) is pretty much guaranteed a Nobel, so the race is on.
If we still don't find anything in ~10 years, then we probably need to go back to the whiteboard and figure out something else.
Shameless self-plug: I'm going to discuss this more in an upcoming episode of my podcast.
ad 3: Plenty of people are working on modified models, such as alternatives to general relativity. There are papers coming out every week. https://en.wikipedia.org/wiki/...
ad 2: Errors in measurements can be somewhat excluded as a possibility because many different measurements looking at different aspects and scales find the same result. Wikipedia lists 3.1 Galaxy rotation curves, 3.2 Velocity dispersions of galaxies, 3.3 Galaxy clusters and gravitational lensing, 3.4 Cosmic microwave background, 3.5 Sky surveys and baryon acoustic oscillations, 3.6 Type Ia supernovae distance measurements, 3.7 Lyman-alpha forest and 3.8 Structure formation . See also my other post.
NB: The message above might reflect my opinion right now, but not necessarily tomorrow or next year.
Because to physicists who spend their time working this problem seem to agree that 1 is most likely. 3 is being attacked all the time with new theories but it is sort of an unlimited well of human imagination.
In my opinion, it is like the WTC "theories". They get started because some yokel cannot understand the official explanations when others seem as likely. However, if you pick up Popular Mechanics book "Debunking 9/11 Myths" (especially the newer addition), they pretty much destroy the reigning alternative alleged theories. Why should I accept the book's version? Because they worked with scientists, engineers, and demolition experts who concur on the official explanation. Why do I not accept the alternative theories? Because they have little scientific analysis backing them. So I bow to the physicists who work the dark matter issue as being the experts and in a much better position to judge because, as intelligent and wonderful as I believe myself to be, I don't have their expertise.
The scientific establishment nurtures contrarians just fine, but they have to play by the same rules as the rest of the community when it comes to backing up their claims and fitting them to the rest of existing data, which is what the armchairs and the crackpots do not wish to do.
Scientists are looking into 2 and 3 just as much. 2 tends to not get much attention since that tends to be dull and very detailed work, but piece by piece possible errors have been eliminated or corrected. 3 and 1 are the same basic problem, there is an error somewhere but figuring out where has proven difficult. Several models have been proposed, but that involves either exotic matter not covered by current models or adjustment for new phenomena. Wondering why they have not been ruled out demonstrates lack of domain knowledge and awareness of what is being worked on, not a flaw in how it is being approached in research.
Europe taking credit for something NASA did? That never happens.
I think that's an honest question instead of a troll. Roughly once a month there's a paper published proposing something along the lines of (2) or (3), mostly (3). However, well, all of the competing theories have fallen apart when compared to newer observations. Dark Matter isn't a great theory. It's not a strong theory, in fact, like you said, it's in a large way a placeholder. However, your assertion that we take it "literally" must be understood in the context of "matter is composed of particles" at a very, very fundamental level. Even things that you think of as "not particles" like radio waves, physicists view as particles; photons in this case. However, photons, having no mass, can't answer that question. So, there has to be some, presumably baryonic, particle that has mass and we haven't observed yet. There are a few good theories suggesting WIMPs (weakly interacting particles) that are a new category of particle that would be hard to detect, but we don't yet have a solid foundation to say they should or should not exist. Hopefully the LHC will either demonstrate or exclude several classes of WIMPs in the next set of experiments.
Wondering why they have not been ruled out demonstrates lack of domain knowledge and awareness of what is being worked on, not a flaw in how it is being approached in research.
Has nothing to do with lack of domain knowledge. You almost NEVER hear physicists talking about dark matter in the public discourse as a possible modeling error. They ALWAYS refer to it as matter we cannot see. Heck the term dark matter itself strongly implies that they think it actually is matter. Otherwise why call it "matter"? I could be cynical and point out that hunting for model errors isn't a great way to get funding for the next particle accelerator but I don't think that is what is going on here. I think those in the field are perfectly well aware that it could be a modeling or measurement error but that's not very interesting or glamorous and so they never talk about it.
Great, the Universe masturbates.
When Fascism comes to America, it will call itself Anti-Fascism, and tell you to give up your guns.
They said that, but 64c (or even 216c) isn't really fast enough to see some of the things that supposedly happened. 64c means three weeks to alphacent, or five months to Vega, as I recall. They were tooling around much faster than that....
"I do not agree with what you say, but I will defend to the death your right to say it"
The bullet cluster and similar observations do constrain it pretty strongly to behave as though the anomaly has momentum in some sense, though. Positing "Oh hey, there's a particle out there that interacts with baryonic matter at a rate similar to neutrinos, but is heavier and slower" vs. "Gravity can, in some cases, happen based on where matter /would/ have been if it didn't hit something". Explaining gravitational lensing where a galaxy /would/ have been via a change in the model of gravity is a bit of an extreme step, and so far "the more probable explanation is the simpler one that explains the observation" has served us pretty well.
Plenty of people are working on modified models, such as alternatives to general relativity. There are papers coming out every week.
And yet they are basically never discussed when the topic comes up in the public discourse. I cannot remember the last time I saw a physicist talking about dark matter as a possible modeling error. I'm certain they do but the notion of dark matter actually being matter dominates the public discourse. Not shocking since it is by far the most interesting of the possible results but still...
Errors in measurements can be somewhat excluded as a possibility because many different measurements looking at different aspects and scales find the same result.
In many cases yes but certainly not off the table. Particularly if some key pieces of the puzzle turn out to be wrong. For (random made up) example if so called standard candles turn out to be not so standard after all. Unlikely I know but stranger things have come to pass.
Electromagnetic force created chemical bonds and the illusion of substance in normal matter. Even though normal matter is 99.9999% "empty", EM chemical bonds keeps solids and liquids from interpenetrating each other. Since dark matter doesnt seem to have EM chemical bonds, it just difuses through the general emptiness of normal matter. It just may make us feel a little heavier than were really are from just normal matter.
It's ALIVE! We must immolate ourselves before it finds us!
They never stop to think that GR may actually be incomplete as a theory.
Except the for the multiple, respected research groups still researching alternatives to GR, the conferences that those groups and other speak at, and even the textbooks that make references and discuss work on alternatives to GR. And it would be hard to assume the way above average attendance at colloquium talks on things like MOND or TeVeS means none of the physicists or astronomers there think about that possibility.
I've posted it before and I'll post it again:
What if the space "sheet" came pre-dimpled, and the "dark matter" that we're seeing is actually the gravitational effect of a dimple that happens to be occupied by a galaxy because it's the local gravity well, rather than the other way around that there's a local gravity well because of the galaxy occupying the space. If the galaxy was to instantaneously vanish (or less magically, have its mass rapidly ejected due to a collision) the dimple would remain.
It's probably not wise to put a lot of weight on a discovery that is only 2.5 sigma.
Umm No. General Relativity's whole "mass distorts space time" thing kind of does explain what makes things move. As opposed to Newtonian physics that only mathematically (and inaccurately at stellar mass scales) predicted how things should move. That's not to say that through the Scientific Method we will not continue to learn new and interesting things. But GR does offer an explanation of what makes things move.
The USA is only 4X older than me...perspective
Ideas like this have been discussed, including even more far out versions that gravity could leak over from other branes, meaning there might be spots of stronger gravity due to things other than the distribution of matter in our view. I have not see news of how such predictions match observation, but it seems it would be tricky to account for galaxy collisions where the dark matter doesn't lag behind.
There's pretty much no predictive power to this idea (other than somewhere there may be a gravitational lens with little to no non-dark matter within it yet). Any galaxies that don't have dark matter just indicate that they formed under their own gravitation, without a dimple.
If such an effect is discovered it'll be used to hang all sorts of really cool crackpot ideas as to its cause and effects. They'd probably be directly related to universal expansion (space expands up and out of the dimple from whatever is at the bottom of it - especially if we can find evidence that our galaxy is in such a dimple).
All this is just mutterings of someone who's read too much scifi, not an astronomer at all, so it's entirely possible it's been proven wrong over and over and I just don't know about it.
It'll be a cold day in hell before you convince me that vaccinations didn't cause the extinction of dinosaurs 6,000 years ago
Sigger than your average
Any chance the topology of space-time can vary independently of gravity?
Despite its flaws, let's use the rubber sheet analogy. Except in this case, suppose there are two rubber sheets: one atop another. Say ordinary matter (planets, stars, etc.) indent the top sheet as expected, but only black holes can over-extend the first sheet and influence the shape of the second underlying sheet.
Now suppose this second sheet deforms over greater distances than the first, which in turn influences the shape of the top sheet overlaying it.
Thoughts?
I'm waiting for someone to explain why so many seem so sure that it actually is some form of exotic matter.
You'll forgive me for believing that that is a lie, because this has been explained many, many times. On the balance of probabilities, you are an irrational nutjob who is resistant to any actual explanation or evidence.
That said, I'll waste few minutes of my precious time pretending your question is sincere and you have a non-zero chance of changing your mind.
The reason why we focus on exotic matter is because observational evidence for a source of anomalous gravitational attraction is robust and diverse and alternative theories have either failed to account for it, or have failed other observational tests.
It isn't as if we have a single measurement on one system. We have detailed measurements of the rotation curves of many spiral galaxies. We have the motion of galaxies in clusters. We have the motion of clusters themselves. We have gravitational lensing studies--which probe the dark matter distribution in a completely different way from dynamical studies. We have cosmological simulations that can't explain galaxy formation without dark matter. We have structure in the cosmic microwave background that is evidence for dark matter, in that it can be explained easily with it, but only with great difficulty without, just as hearing a dog bark is evidence for a dog because a dog easily explains barking, while alternative explanations have much lower priors and so are less plausible. To deny this is to deny Bayes.
Did I have to dig deeply into some mysterious literature to find this? No. I had to look at Wikipedia: https://en.wikipedia.org/wiki/...
Do you see why I think your question is dishonest?
So that makes "maybe the measurements are in error" much less plausible than "dark matter exists".
With regard to new physics, the problem is that the low-hanging fruit have been picked, and what remains has a hard time explaining all the diverse observational evidence. It is hard to find a theory that explains all the phenomena that are observed that is not "there is some kind of exotic matter out there". None-the-less, we are actively testing a few such theories. Again from Wikipedia: https://en.wikipedia.org/wiki/...
So now your question has been answered. You need wait no more. You can either change your mind, and agree that dark matter is the most plausible explanation of the robust and diverse observations, or you can explain why you find some alternative hypothesis more plausible. But you can never again honestly ask, "Why don't people take observational error or alternative theories more seriously?"
Blasphemy is a human right. Blasphemophobia kills.
You'll forgive me for believing that that is a lie, because this has been explained many, many times. On the balance of probabilities, you are an irrational nutjob who is resistant to any actual explanation or evidence.
And based on your statement you'll forgive me for believing that you are a condescending asshole who looks down on people who ask a pretty straightforward question.
That said, I'll waste few minutes of my precious time pretending your question is sincere and you have a non-zero chance of changing your mind.
And the condescending asshole theory is confirmed. "Your precious time"? You're posting on slashdot. If you actually had better things to do you wouldn't be here. So drop the attitude. I didn't come here to insult you so I'd appreciate the same consideration.
Do you see why I think your question is dishonest?
I see that you are a condescending person who thinks I'm asking this question for reasons other than intellectual curiosity. You think it is "dishonest" to question why someone would strongly favor a hypothesis for which there is only indirect evidence and there are alternatives which haven't been ruled out? Curious logic you have there.
The reason why we focus on exotic matter is because observational evidence for a source of anomalous gravitational attraction is robust and diverse and alternative theories have either failed to account for it, or have failed other observational tests.
We have evidence that something in our model of the gravitational attraction in the universe is incomplete based on observations but have zero direct evidence of any actual exotic matter. The fact that we've tried theories other than exotic matter that have not panned out is evidence of nothing other than the fact that those particular theories were wrong. I don't doubt that some form of exotic matter is a very reasonable explanation but claiming it is the most plausible answer given the lack of direct evidence is illogical at this time. And it certainly doesn't excuse scientists from very often leaving out disclaimers that we really have no idea what dark matter is and that exotic matter is merely plausible but unconfirmed.
You can either change your mind, and agree that dark matter is the most plausible explanation of the robust and diverse observations, or you can explain why you find some alternative hypothesis more plausible.
I don't favor any particular hypothesis. Any answer we ultimately get to the question will be fascinating whether it be exotic matter or a revolutionary model of gravitation. Given that there is no actual direct evidence of exotic matter I remain unconvinced that exotic matter is any more or less plausible than other forms of modeling error. If you favor that particular hypothesis that's fine but don't pretend that you actually know the answer. If your point is that physicists favor exotic matter simple because the other theories haven't panned out then that's fine but you could have said that in one sentence without the insults or the attitude.
That you effortlessly use words like "armchairs" and "crackpots", rather proves my point that contrarians aren't to be tolerated.
You've also proved my point. The class "contrarians" consists of the most extreme examples you can think of.
Armchair physicists are not necessarily contrarian though, but just a large group of people who are too lazy to follow through on or check any of the claims they make, but speak with certainty as if their baseless claims are on level or superior to those that spend considerable effort trying to check claims before making them with any certainty.
Papers and talks that go against mainstream theories are pretty common, but often include some attempt at detailed calculations to address at least one category of observation and often have a lot of qualifiers or caveats given about things that have yet to be checked. They also make rather specific, quantified claims, instead of vague ones.
He was simply taking a contrarian approach to your view that they should ;)
Sigger than your average
2 and 3 are less and less likely because there is observational evidence of dark matter using different methods. e.g. rotation of galaxy and lensing which are different observations, but point to one cause which is increased mass of matter that's not detectable in the electromagnetic spectrum.
There's a high bar to demonstrate your competence, which is how is should be. We can't let idiots who know fuck all about the subject matter dominate the debate. Sorry.
I do not want your cheap brainburning drugs. They are useless for work. And I am a working man today.
They never stop to think that GR may actually be incomplete as a theory.
Wrong. The jaggy discrete quantum world and its forces are completely alien to GR. No-one denies this. Your statement is profoundly ignorant.
I do not want your cheap brainburning drugs. They are useless for work. And I am a working man today.
Now that you've posted it twice, you can probably give it a rest.
I do not want your cheap brainburning drugs. They are useless for work. And I am a working man today.
Invisible mass of magic particles? Doesn't that describe a neutrino burst? What's magic about something like slow massive neutrinos?
Heck, do you believe in trans-Saturnian planets? It turned out that Saturn had some discrepancies with its predicted orbit. Rather than trying to hack Newtonian gravitation, astronomers figured that they'd be accounted for by a more distant planet with certain characteristics, and found Uranus. Neptune was found much the same way.
"When you have eliminated the unacceptable, whatever is left, however improbable, must be the truthiness" - Holmes
They do as long as they don't propose anything too radical.. like that dark matter might fit very well as tachyonic material. They cant even consider that because it threatens fundamental scripture. ...
Below the speed of light Special Relativity is one of the most accurate theories in physics - above the speed of light..
No actually the real problem is that general relativity is completely wrong, at least at FTL speeds. If you actually build an FTL version of physics it becomes quite clear that an absolute frame and FTL Simultaneity are required for the universe to exist, and general relativity forbids both. The solution that reconciles the two models is to restrict the (physical) dimension of time to quantum scales. This marginally modifies the theory of space time to make dimensional time a notional abstract quantity.
The real problem with an FTL physics is that it lets the 'demons' of infinite numbers into the maths, and so requires a completely new approach. Which is why so many physicists hate it so much. (Working in Strong AI I have developed a maths that basically works with infinite numbers and imaginary roots.)
Below the speed of light Special Relativity is one of the most accurate theories in physics - above the speed of light..
I have developed a maths that basically works with infinite numbers and imaginary roots.
Welcome to an intro level abstract algebra course taken by freshman or sophomore math majors. And dealing with infinities spills over into work with QFT and theories derived from it.
. like that dark matter might fit very well as tachyonic material. They cant even consider that because it threatens fundamental scripture. ...
Every so often a Lorentz symmetry violating extension to the Standard Model pops up and researchers have had no problem giving well received talks on the implications of these, including if the proposed new particles or regular particles behaving differently can account for dark matter. Maybe before calling people out basing their views on "fundamental scripture" you should consider if your own view of what people actually do has been determined your own beliefs disjoint from reality.
The reason you don't understand is that your too lazy to read anything about outside a /. summary.
If information wants to be free, why does my internet connection cost so much?