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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?
Except what they're talking about is an anomaly in Relativity at larger scales. There's no evidence so far the anomaly is caused by some invisible mass of magic particles.
"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."
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!
I smell a typo? Maybe the dark matter is behind 5 light years?
Thank you, Bradley Manning, Edward Snowden and so many others, for courageously defending humanity, my freedom and more!
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.
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."
"that dark matter may well interact with itself" — this is just quid pro quo in the halls of Congress.
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.
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.
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.
For successFul
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.
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!
It's probably not wise to put a lot of weight on a discovery that is only 2.5 sigma.
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.
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.
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?