Dark Matter Discovered 386
sebFlyte writes "Wired is reporting that scientists have come up to a solution as to where all the matter in the universe actually is. Experiments being done with Chandra, NASA's X-ray telescope have shown up a likely candidate for the solution of the dark matter problem. There are massive quantities of Baryons in a super-heated gas cloud several hundred million light years away."
But what about galactic cohesion? (Score:2, Interesting)
These clouds are great for a macro-framework missing mass solution but unless they are found to exist in a somewhat smooth (or central) distribution in a galaxy how would massive clouds several hundred million light years away provide a solution for cases like this?
Huntred
Re:Wait a sec, this story isn't about "dark matter (Score:3, Interesting)
Which is what they're constantly doing. I heard the theories in my astronomy class. There's plenty of them, such as brown dwarves just drifting around out there. How do you explain them? Well some star has a vector or some light appears bent (lens effect) and it's figured there's some large enough object out there not emitting light which is doing it. And who's to say it isn't large amounts effectively of bits the size of pea gravel drifting around?
In other words, if regular stuff is about 5% of the energy density of the universe, with dark matter at about 20%, and dark energy at about 75% -- the stuff in this story comes into that 5%, ie, regular stuff and not dark matter.
Dark matter is, as I understood, matter which isn't emitting some radiation, i.e. visible light or gamma rays. It's predicted, because without something being somewhere a number would be +0.0000150 instead of +0.0000146 and we can pretty much drop the old Intel Pentium jokes.
Re:Wait a sec, this story isn't about "dark matter (Score:2, Interesting)
Re:Aren't baryons just normal matter? (Score:5, Interesting)
First, I had to look up "tachyon". You are right, tachyons are apparently particles that travel faster than the speed of light. I've only heard the term from Star Trek, and for the time being that's where these particles are from - the realm of (science) fiction. I've certainly never had them mentioned in class!
Baryons are not the counterpart to tachyons. Baryons are simply particles that are made up of quarks. The two best known examples are neutrons and protons, which make up virtually all of the stuff you own. Yes, baryonic matter is pretty much everything we interact with.
Two examples of particles that are very common and all around us are electrons and neutrinos. You're familiar with electrons (which are not baryons!), and the nuclear reactions in the Sun are constantly producing a mind-boggling number of neutrinos. Generated in the centre, they travel at nearly the speed of light which means that the ones passing through your body right now are about 8 minutes old. By comparison, the light from the Sun (photons, also not baryons) bounces off all the photons there, so by the time it actually reaches you it's about a million years old.
Finally, and most importantly, dark matter has not been discovered. You are also right in that the reporter is very much out of his depth. The article states that there is evidence for baryons to be found in places where we have not seen them before. What's one theory as to how they got there? Dark matter.
Re:This is BS - Dark Matter is Fiction (Score:2, Interesting)
http://www.astro.ucla.edu/~wright/lerner_errors.ht ml [ucla.edu]
And one word on theories. The Big Bang, gravity, evolution... all fit under the category of theories. No good scientist will argue with that. But the thing about these theories - for everything we've thrown at them so far, they work. They hold up. They may need modifications, tinkering (e.g. gravity has yet to be married to quantum mechanics), but the foundation is very solid.
Re:The premise of Dark Matter is flawed... (Score:2, Interesting)
The existence of "dark matter"
Dark matter, or "non-baryonic" matter is a hypothetical form of matter different from any observed on Earth but which is nonetheless required by the Big Bang. Current versions of the (ever-changing) theory require that total gravitating matter density be equal to 0.3 of the critical density but that of ordinary, baryon matter be only 0.05 of the critical density. This means that 0.25 of the critical density has to be in the form of some undiscovered, non-baryonic matter, generally described as Wimps, weakly interacting massive particles.
This "cold dark matter" or CDM, was hypothesized as essential for the Big Bang theory back in 1980--23 years ago. Since then physicists have searched diligently with dozens of experiments for any evidence of the existence of these dark matter particle here on Earth. Oddly enough every one of the experiments has had negative results. In fields of research other than cosmology this would have long ago led to the conclusion that CDM does not exist. But Big Bang cosmology does not taken "NO" for an answer. So the failure to find the CDM after so many experiments does not in any way shake the faith of Big Bangers in such CDM. This is evidence that what we are dealing with here is a religious faith, not a scientific theory that can be refuted by experiment or observation.
The idea that neutrinos might form a bath of Hot Dark Matter has also been undermined by experiments that indicate that while neutrons do probably have some mass, it is of the order of 0.1 eV (energy equivalent), which means that total neutrino mass in the universe is likely to be around one tenth of the mass of ordinary matter.
Wright argues that the existence of dark matter if proved by the difference between the total gravitating mass inferred for galaxies and cluster of galaxies and the mass in observable stars. But this is an absurd non-sequitor. Observations have demonstrated that stars constitute only a small fraction of the total mass of ordinary matter that can be observed. In clusters of galaxies we can observe by X-ray emissions huge clouds of hot plasma, which have masses far greater than that of bright stars.
There is extensive observational evidence for ordinary matter in two other forms that are relatively dim, One is white dwarfs in the halos of spiral galaxies. Recent observations of high proper motion stars have shown that halo white dwarfs constitute a mass of about 1011 solar masses, comparable to about half the total estimated mass of the Galaxy [R.A. Mendez and D. Minnitti
Observations of ultraviolet and soft x-ray absorption has revealed the existence of "warm plasma' with a temperature of only about 0.2keV, which amounts to a mass comparable to that of the entire Local group of galaxies.(Nature 421, 719). If we adds up the warm plasma, which is sufficiently dim to be observable only as it absorbs radiation from more dint objects, the hot plasma, and the white dwarfs, we have enough matter to equal that which is inferred by the gravitational mass of cluster of galaxies. So there is no need for non-baryonic matter and there is no room for it either.
Conclusion: the evidence against the existence of non-baryonic"dark" matter is stronger than ever. Ordinary matter is only the only type of matter that exists.
For further evidence (taken from http://www.skepticalinvestigations.org/controversi es/bigbang.htm):
Re:Ummm (Score:4, Interesting)
What I was trying to point out, but evidently with little success, was that the article was hyping the discovery. It is certainly important (as you might gather from the fact that it is being published in Nature). The article, however, summarizes the physicists' findings but allows the reader to think that the "dark matter" that the article refers to is that really mysterious stuff that science fiction writers like to write about, not the less mysterious stuff that the physicists were actually talking about.
And, by the way, dark energy (which indeed is horribly named) is a huge mystery. Ask a particle physicist to calculate the vacuum energy density and he will give you an answer that is incorrect by many, many, MANY orders of magnitude. See http://www.site.uottawa.ca:4321/astronomy/index.h
Re:But what about galactic cohesion? (Score:3, Interesting)
Galaxy rotation velocity curve Java applet explains this problem. [queensu.ca]
Baryonic vs. non-baryonic dark matter (Score:2, Interesting)
But most of the 4% baryonic matter is not stars, or easily visible gas and dust. It's made of normal stuff, but also dark - baryonic dark matter. That's what's under discussion here.
Even if this points the way to all of the baryonic dark matter, the 23% non-baryonic dark matter and the 73% dark energy still need accounting for. So you don't have to find _all_ the kinds of dark matter to have discovered some of the dark matter, and there's nothing wrong with the headline.
(Missing mass and dark matter, by the way, are pretty much synonyms.)
Re:Wrong Name (Score:4, Interesting)
The counterargument (Score:3, Interesting)
Clearly not all matter is in stars, so if that is your definition, then some dark matter must exist. My BS subject refered to the theories that dark matter must be something undiscovered, because we can't seem to find enough to fit the Big Bang theory's predictions. I remain convinced that the percentage of dark matter necessary to make Omega equal to 1 does not fit with observation.
I don't pretend to know what the correct theory is, but I am convinced that the Big Bang is not accurate, and that there are forces/processes at work in the cosmos that are being thrown out prematurely because they contradict the Big Bang, thus preventing the most accurate theory from surfacing. Ned Wright's defenses and criticisms are not the open-minded evaluation that I was looking for.
--Sandy
Re:Wait a sec, this story isn't about "dark matter (Score:2, Interesting)
That's because intergalactic baryons not only fill a gap in scientists' understanding of the universe, but they may also lead to a better understanding of "dark matter," a mysterious and unseen form of matter that has so far only been detected by the gravitational pull it exerts on other bodies in the universe. "If we are right, each single one of these filaments is connected to a cloud of dark matter," said Nicastro. "If there wasn't dark matter there, or something with strong gravity that pulled on the matter in these filaments, we wouldn't have galaxies or filaments." Rather, the baryons would be pulled into galaxies and the galaxies into each other.
Basically speaking it could be that the reason this big cloud of baryons hasn't collapsed into stars is because of dark matter.
Re:Maybe its a big fudge (Score:4, Interesting)
2. Several ways --- rotation, motion of a number of satellite galaxies, mass/light ratio, Tully-Fisher relation, and, if it's a spiral, simply by the size if we know the distance (this is pretty rough, but a decent indicator)
3. Within a galaxy, I don't think so. But intra-galactic dark matter is just one type. There is also non-luminous matter in between galaxies in clusters to account for their motion. Hot X-ray gas is one candidate, but I thought I remembered that there didn't seem to be enough of that stuff to account for cluster dynamics. Maybe this new stuff will help out, though the mass deficit was much more than this 2% if I recall correctly, and is probably non-baryonic.
3. Yes, they should. That's the problem. Outer stars and globular clusters are orbiting way to fast if all the mass in the galaxy is traced by luminous matter. A good model to account for the rotational behavior is a spherical halo (not just a disk) of non-luminous matter. This is the intra-galactic dark matter, and not relevant to the article.
Re:Wait a sec, this story isn't about "dark matter (Score:5, Interesting)
The story is a bit about dark matter, because there is a dark matter presence implied by the newly discovered gas clouds. But that's no surprise - the observed structure of ordinary galaxies already implies that they as well are permeated with dark matter.
Re:Wait a sec, this story isn't about "dark matter (Score:5, Interesting)
There sure is dark matter out there that we don't understand well at all, and probably more than one kind. Neutrinos are one form, since recent experiments indicate they do have some mass. Neutrinos are pretty exotic compared to normal baryonic matter. There may well be weirder stuff.
Agree with you though, that Star Trek overdoes it.
Re:Ummm (Score:4, Interesting)
While we have some ideas about the non-baryonic dark matter that might pan out soon, indeed, we're clueless about the dark energy in a very profound way.
Re:Wait a sec, this story isn't about "dark matter (Score:2, Interesting)
Seriously: We can model the solar system quite well using only the derived* masses of planets to within a few percentage points per thousand years... Yet supposedly the universe has some random form of gravitational energy which accounts for over 80% of the 'mass'. Get real.
Non-baryonic matter is the luminiferous aether of today.
If I'm wrong, great. But the whole theory stinks of hand-waving. Just becuase you don't have a clue doesn't mean you invent some wild theory -- not when there are dozesn of equally (or more) likely, simple explinations.
Every few years somebody finds another few percent of the 'missing' matter. I'm just waiting.... For some good evidence to satisfy my cynacal nature, or for them to get up to about 90% so that I can openly mock the concept.
For now I do admit that, in general, I don't know more about physicsthan the average masters holder therein; I do, however, know a LOT about gravity -- enough to make me question everything about non-baryonic matter anyway.
*It would be incredibly unlikely that we could 'accidentally' account for any matter/mass from the observational methods by which we derived the present, assumed masses for the planets.
Re:Wrong Name (Score:5, Interesting)
YOu gotta admit, though... There really isn't a good explanation of why gravity SHOULDN'T change over vast distances.
F=ma = G*M*m/(r^2) -- 'G' is derived observationally. Only a few hundred years of observation tell us that it is a constant. Only a few dozen of those actually FROM SPACE -- Perhaps a few hundred years more will show that it is proportional to some (presumambly negative) exponent of 'r' (distance). Perhaps not.
I admit to preferring MOND over imaginary matter. However, what I like the most is that the guys have open minds... unlike the typical 'scientist' favoring NB matter -- a bad hypothesis usually treated as sound theory. If NB matter were treated with the caution that MOND is, I would enjoy reading about it. Instead most authors treat it as assumed fact and build upon it. Bah. Excel can curve fit data; doesn't mean I assume a random scatter plot can be modeled by a 4th order equation.
I had this idea (Score:2, Interesting)
OK, lets be honest: I haven't read the article. Still, with the mention of 'dark matter,' I thought I'd ask the opinion of my fellow /.'rs.
From what I understand, the theory of 'dark matter' is the way we explain the existence of forces that seem to have no originating matter. We see the effects, but don't see the matter that is causing it. So we say that there is 'dark matter.'
Fast forward a few decades. We have this new thing called string theory. One part of string theory is that our force of gravity is not, as it seems, a force inferior to our other forces, but that gravity 'strings' do not have endpoints on our own plane, but in stead loop back upon themselves. This allows for the idea of gravity 'leaking' from our plane into parallel dimensions.
Here is my idea: if gravity can leak from our plane to parallel dimensions, isn't it plausable that forces might leak from parallel dimensions into our plane? Wouldn't that explain the apparently massless forces that we observe?
Rethinking Newton on Large Scales... (Score:3, Interesting)
ZERO is what MOND [MOdified Newtonian Dynamics] predicts because if the compact nature of the galaxy in question, it is still in the Newtonian regime.
It's time to reconsider Newton on large scales.