Ring Of Stars Found Around Milky Way 231
LoPingHo writes "Scientists have found a ring of stars around our galaxy that has previously been undetected due to the faintness of the stars. The article says that it only amounts to 1% of the galaxies mass, but if they are just now finding those, that means there could be even fainter ones there too. Could this be part of the elusive 'dark matter' talked about so much lately?"
Thanks! (Score:2, Funny)
Dark Matter? (Score:4, Insightful)
Re:Dark Matter? (Score:3, Insightful)
Re:Dark Matter? (Score:3, Informative)
Cool baryonic matter not emitting much light has been eliminated from the possibility of accounting for all the "missing mass". A more promising idea is something non-baryonic but massive, like a massive neutrino. Well, more actually than just one of those.
For more information try google "non-baryonic dark.matter" or "baryonic dark.matter".
It's amazing really, astronomy is still at the forefront of physics here on earth, when they figure out what dark matter is and can reproduce that here on earth, it's likely to be one of the biggest things in physics (for a while).
Re:Dark Matter? (Score:4, Informative)
Could you provide some sort of support for that claim?
There are two realms of explanation for the supposed enigma of Dark Matter. One is that matter like these stars have simply escaped our detection; in short, that it is our instruments that are at fault. The other is that our instruments have reached perfection (at detecting the things we can explain), and we've looked everywhere, and, well, supermassive and invisible objects exist all over the place.
The latter is a pretty theory, appealing to the imagination and to the egos of scientists. It's also completely ludicrous as the sole explanation for observed mass/gravity discrepancies. A few years ago, scientists barely thought brown dwarf stars existed. Now we know that they're everywhere, and in all likelihood far more prevalent than scientists currently have the capacity to investigate. What else are they missing?
These things are hard to see across the vastness of space, especially when they emit little or not light. That doesn't mean they aren't there. As .. improbable (coughhackcough) as it might seem to some, it's far more likely that our instruments just aren't strong enough. That's all.
Re:Dark Matter? (Score:3, Insightful)
This was an interesting read [princeton.edu], though as I said, it was found just through a google search.
I admit it's all speculation and half of it I don't claim to actually understand to the level of making a good argument.
But think of a couple things. One, it's not about perfect instruments, it's about instruments that are good enough to see what you are looking for. If I have ten marbles in a dish, but it weighs as much as twenty... I know I should see the extra marbles if they are ordinary marbles. We are not talking about a little bit of missing mass, we are talking about a huge bit of missing mass.
Another, it's about what you do see. For example, there cannot be a diffuse gas in the galaxies to cause this effect because (a) it would not have enough mass and (b) you could see absorption lines of the gas.
It's not like we are looking for something small, remember... we're looking for something big! Something with a lot of mass that for some reason doesn't or can't glow.
And of course I agree that relatively exotic dark matter cannot be the only source of dark matter, some is just undetected baryonic matter. The rub is that it doesn't seem there could be enough of that to account for all the dark matter, a significan portion looks to be something exotic or at least non-baryonic.
Re:Dark Matter? (Score:4, Informative)
Aside: Really, it's not about the egos of scientists, or the perfection of our telescopes and instruments. Goodness knows, if they were so perfect, we wouldn't be begging for money to build new and better ones! :)
The link that pyrrho mentioned [princeton.edu] describes the basic reasons why baryons can't be all of the hypothesized dark matter. And since 1996 (when the article was written), the evidence has become vastly more convincing. I'll attempt to summarize.
Sure, we could hypothesize that the Universe is filled with "dim, normal stuff" like brown dwarfs, white dwarfs, lost airline luggage, missing socks, dryer lint... but we're just not able to see them. Fair enough. But there is a limit to this argument for numerous reasons.
Okay, so maybe we just live in an empty, open Universe! But numerous measurements of the curvature of the Universe, in particular recent observations of the cosmic microwave background itself suggest that the curvature is not open but uncurved. So we live in a Universe with plenty of gravitational matter of some form or another. Aside: we are gathering a huge amount of information by looking at the angular sizes of the bumps and dips in the cosmic microwave background, which is fossil radiation from the Big Bang and a few percent of the static you see on your TV when tuned to a blank UHF channel. This page [upenn.edu] shows what the CMB power spectra (that is, how many inhomogeneities occur at a given angular size) look like, and how changing various cosmological parameters has an effect on the spectrum you'd expect to see. Try out changing the baryon density -- the effect is quite pronounced. It also says that the Universe has the number of baryons that Big Bang theory says it should have.
So this makes us all feel a bit uncomfortable, because either some of the fundamental tenets of cosmology are flawed (even though they explain nearly all of the observable Universe, right down to the abundances of the elements and the large scale structure of galaxies and the cosmic microwave background, the recession of galaxies etc.) ... OR ... the Universe is mostly filled with matter what is unlike anything we yet know how to explain.
It's going to be a fun ride! :)
Re:Dark Matter? (Score:3, Informative)
Dark matter has been invoked to explain puzzling observations, within a theoretical framework that has proven pretty trustworthy for everything else so far. Either dark matter is real, or the framework needs a facelift somewhere. Jury's still out on that one.
Let's highlight one example. Consider first the motion of the planets around the Sun, which itself comprises most of the mass of the Solar System. The innermost planets like Mercury and Venus are whizzing around at high speeds to maintain their close orbits. By the time you get out to Neptune or Pluto, they're just crawling along, since they are far away from the Sun. This is all nice and reasonable.
Now when you look at (spiral) galaxies, most of their luminosity (and presumably mass) comes from their inner regions, so you might expect the same kind of rotation pattern; the inner regions would have high rotational velocities, and the outer regions would rotate slowly. But this doesn't happen -- in fact the outer regions tend to rotate every bit as fast as the inner regions! But there's no luminous matter out there to support such rapid motion! There must be something out there that has huge gravitational impact, but without emitting any kind of light. Hence one invocation of dark matter. There are others, but the theme is largely the same.
Some folks understandably find the notion of dark matter distasteful, and are working on modified theories of gravity that have 'appropriate' characteristics on the scale of an entire galaxy. But many consider those "modified gravity" arguments to be unconvincing, ad hoc and distasteful in their own way -- so far.
What is important is that we are learning more and more about our place in the Universe, and uncovering new puzzles that we don't yet understand. And that's what makes it fun.
Re:Dark Matter? (Score:5, Informative)
Re:Dark Matter? (Score:2)
Re:Dark Matter? (Score:3, Informative)
Nope. When the dark matter problem was first discovered they thought (hoped) that it was just normal matter that we can't see. It isn't. This post [slashdot.org] provides a pretty good explanation.
Note: that post only lists a few of the reasons. There are several others. Either we've made a whopper of a mistake in our understanding of physics or more than half the mass in the universe is "something else".
-
Re:Dark Matter? (Score:3, Interesting)
obTolkien (Score:3, Funny)
Obligatory Tolkien (consider yourself warned):
Re:obTolkien (Score:5, Funny)
Is that kind of like token Tolkien?
...mmm, the smell of burning karma.
Not Actually Tolkien Ring (Score:2)
Real explanation (Score:5, Funny)
As for the missing mass, that's due to Elmer FUD.
Ring of stars (Score:5, Interesting)
Re:Ring of stars (Score:2)
Re:Ring of stars (Score:5, Informative)
I believe that a Kemplerer Rosette is characterized as being a stable gravitational configuration of bpdoes orbiting a single point at similar distances and speeds in such a way that all bodies are equidistant, and is further characterized in that one could envision a regular polygon of n-sides, where n is the number of bodies, and if one vertex is mapped to the location of one body, and the center of the polygon is mapped to the common orbit location, then all other vertexes will correspond to locations where the other bodies reside.
This ring of stars, being randomly located, would not qualify. In addition, a Kemplerer Rosette is only stable against small perturbations; if the bodies are far enough apart that other gravitational influences grow large with respect to their gravitational influence on each other, then it is no longer stable.
Re:Ring of stars (Score:2)
Actually I made it up on the spot out of memory. Of course, it helps that I modelled them for high school physics class... that and I read all of Niven's books...
Re:Ring of stars (Score:2, Informative)
1. The Universe is finite[1] and there are parts of the Universe that we know to be devoid of mass[2]. The mass in the Universe must therefore be finite.
2. Take a sample region of the Universe. Tally up the amount of visible mass. This gives you a density. Multiply this by the known volume of the Universe[3].
3. Matter is energy. Energy is matter. If antimatter existed in the same quantities as matter, there'd be no you, no me, nothing, nada, rien. Fortunately, antimatter only exists naturally in small quantities[5][6].
[1] There is only so far a photon can travel from one 'edge' of the Universe so the Universe is essentially finite ;) :P
[2] ie, vacuums
[3] Assume homogeneity first of course[4]
[4] Not necessarily a bad assumption given the uniformity of the Cosmic Microwave Background
[5] And in physics labs around the world
[6] Why antimatter doesn't naturally exist in the same quantities as matter is an interesting question in its own right.
When you said "Ring of Stars"... (Score:2, Funny)
.
??? huh? (Score:2)
so - they found a ring of stars around a bunch of stars?
Re:??? huh? (Score:2)
It's not just that there's a ring of stars around a disk of stars, but that that ring relates to the disk in a particular way, which makes the galaxy bigger than previously thought.
I don't get it (Score:5, Interesting)
Re:I don't get it (Score:4, Informative)
Nobody knows what dark matter is yet, but there are lots of guesses.
Re:I don't get it (Score:2)
Re:I don't get it (Score:2, Interesting)
The dark matter could be due to neutrinos, black holes, WIMPs, planets(non-light emitting matter like you suggested), other universes, or any other number of bizzare things that scientists have hypothesized.
Re:I don't get it (Score:2)
Re:I don't get it (Score:4, Informative)
Tachyon's, the result of solving Einstein's equations for an object travelling faster than light, would have negative mass (but positive energy) and would travel backwards through time. Before you say it, yes its impossible to accelerate to lightspeed. On the other hand, there's no reason a certain class of particles couldn't come into existence at faster than light speeds.
Kaluza-Klein particles, a recent idea, are another option for dark matter. They're so-named because they're believed to travel primarily through the 9 folded-up dimensions of string theory. (Kaluza and Klein devised the mathetical methods and theories which explain how string theory functions in an 11 or 12 dimensional universe). These particles, but flitting in and out of "our" four dimensions would only be weakly interacting (and thus qualify as dark matter) but would interact quite powerfully when they were present (due to extremely high mass).
Re:I don't get it (Score:2)
Still over my head, though.
Re:I don't get it (Score:2)
Re:I don't get it (Score:5, Interesting)
Only according to a theory that assumes c is a constant while it is not - it's getting slower al the time. It's called CDK. This may also very well mean the red-shift calculations used to determine the speed at which galaxies move away from us are totally wrong which may therefore mean that the universe is not expanding at all (or at least not that fast) which makes the mass-calculations bullshit as well and may very well mean dark mass does not exist and there's just nothing out there. This is a good read about it: http://www.ldolphin.org/bowden.html
Re:Warning - Cretinist reference (Score:2)
Apart from that, the CDK theory potentially solves a lot of problems and mysteries about dark matter and the expansion of the universe.
Re:I don't get it (Score:2)
I believe the equation you are referring to is:
E = m*c^2/sqrt(1-v^2/c^2).
If v > c, then (1-v^2/c^2) < 0 and the denominator becomes imaginary. Thus in order for the particle to have real energy it must have imaginary mass.
I think imaginary mass is even harder to envision than negative mass.
Re:I don't get it (Score:2)
I don't think its really all that mysterious or difficult, or that we're really all that smart. But I could be wrong.
Re:I don't get it (Score:3, Insightful)
For instance---and this is entirely fictitious---suppose the galaxies appear to be ten times too small to hold together given how fast they are spinning, and so you conclude they must consist of 90% dark matter that is moons and dust and such. Then, suppose you measure the gravitational lensing, and find that the effective mass is only half what it should be if it were 90% moons and dust. Well, you'd probably have to conclude it's only 40% moons and dust, and 50% pure magic.
That's the kind of thing these scientists do. If someone with actual facts could back me up a bit, I'd appreciate it.
Regardless, it's easy to dismiss a mystery if you don't know the facts involved.
Re:I don't get it (Score:3, Insightful)
Re:I don't get it (Score:2)
here's the problem (Score:4, Interesting)
Others suggest alot of neutron stars spinning around out there, also not likely. We'd have noticed them, either by an inordinate amount of nearby pulsars, or simply from gravitational lensing. Same goes for dead hunks of carbon. To make up the missing mass, there would have to be many of these things. And with many of them, the chance of spotting several would be high.
The macho theory suggests there COULD be a *few* but *extremely* massive objects wandering around out there. Something like supermassive blackholes, or something else. If there were a few, and they emitted no light (likely), then they'd be easy to miss.
The other theory suggests that there is some kind of exotic matter which we haven't discovered yet that emits no known form of radiation, but may indeed generate gravity. This is also possible, as the newly discovered 'dark energy''s origins are also unknown. The confirmation of dark energy (which is recent) is what drives the expansion of the universe, and is indeed some kind of 'anti gravity'. Very interesting, but very strange. And we have no idea where the hell it comes from.
Re:I don't get it (Score:5, Informative)
It turns out that the measured effects of dark matter mean that only a small fraction of it can be "normal" matter. Look up "baryonic" and "non-baryonic" dark matter on Google for more information on the subject.
The "normal" component could be anything from white dwarf stars to brown dwarf super-planets to micro black holes to dust and gas, or all of the above. However, that still leaves most of the mass as something else.
Re:I don't get it (Score:2, Informative)
Re:I don't get it (Score:5, Funny)
Go ahead, ask me another one...
Not Dark matter (Score:5, Informative)
The reason scientists believe that there should be dark matter is because of the fact that the stars on the edge of galaxies move faster than they should. According to the measured amounts of mass in a galaxy, the stars on the edges would fly out of orbit at the speeds they are going.
Extra mass on the outer fringe of a galaxy could not contribute to this lack of gravity. I am pretty sure that more than 1% of the galaxy's mass is missing also. But I suppose this goes to show that we never know as much as we think we do.
Checkout the everything 2 node on dark matter [everything2.com] for more information.
Re:Not Dark matter (Score:3, Informative)
There are currently two theories for what dark matter is. The first is the MACHO theory. MACHO stands for Massive Compact Halo Object. This basically means there are large objects orbit on the outskirts of the milky way. These are large objects which weren't big enough to become stars. They are probably about the mass of Jupiter. We know that at least some MACHO's exist by the way they lense or bend the light from a distant star. Although we have observed lensing, it doesn't occur frequently enough to account for all the mass that needs to be in the outer halo.
The other dark matter theory is for WIMPS. A WIMP is a Weakly Interacting Massive Particle. In this case massive means massive on an atomic scale. These particles have a tendency to not interact with other particles. They also cannot radiate away energy. Because of this they can't lose energy easily and orbit at great distances. This would explain the extra mass needed to sustain the rotation of galaxies.
It will be a long time before we have conclusive evidence as to what dark matter is and whether or not it exists.
the first one about MACHOs basicly the theory was that these big objects "around the edge of the galaxy" caused the faster spin...well if you have stars out there it sort of removes the need for machos...anyway i don't know if this accounts for all the dark matter (1%, a mass of 1 billion suns) but it is a good start.
Re:Not Dark matter (Score:2)
As a mathematical model, MACHO's are great. In reality though, they're simply barionic matter that we can't see, not some exotic particle. The simple explaination is that there are butt loads (Butt, n: any of various units of liquid capacity; especially : a measure equal to 108 imperial gallons, 491 liters)of planets the size of Jupiter surfing the galaxy.
Re:Not Dark matter (Score:2, Insightful)
I mean, these are light-emitting stars, even. What about brown dwarf protostars and even dark clouds of space dust?
The observation that stars at the edge of our galaxy don't move fast enough shouldn't incite scientists to come up with new types of matter--it should incite them to find the matter that they've obviously overlooked.
hmmmm (Score:2)
Re:hmmmm (Score:5, Funny)
The tipoff was that it had trouble maintaining anything other than a straight 4/4 rhythm.
Re:hmmmm (Score:2)
Hmmm... (Score:2)
Space and Science can explain anything... (Score:4, Funny)
I explained to her logically using space and science that "You're right, You're the mom and I'm the son and we all know the world revolves around the sun".
Likewise invisable stars explain dark maatter.
Dark Matter (Score:5, Informative)
In the world of diagnosing dark matter, scientists think that neutrinos could make up a good hunk of it.
http://www.aip.org/enews/physnews/2002/split/58
I heard about this on NPR's Talk of the Nation: Science Friday last week. What i heard was: in order for neutrino's to change from one type to another, they must have a small ammount of mass, and even if you give neutrino's a tiny tiny tiny ammount of mass, they suddenly account for a good hunk of the dark matter out there.
I know nothing about any of this, so if someone could go into further detail it'd be great.
Re:Dark Matter (Score:2)
Any physics majors out there?
Re:Dark Matter (Score:2)
probably not (Score:2)
The reason there can't be many of them is we'd probably have detected them already by gravitational lensing. So whatever it is thats out there, its really heavy, and theres not many of them because so far we havent seen any lensing from objects near the edge of the galaxy.
In order to make up the necessary 'missing matter' from things like faint stars, neutron stars or dead stars, there would need to be alot of them.
While we're on theoretics, its also possible the phenomenon is related to dark energy, which has recently (within the past couple months) been nearly proven to exist by studying several lensing objects. 'Dark Energy' is likely whats responsible for the increasing rate of expansion in the universe. Its effectively a kind of anti-gravity. Its nature, such as where it comes from, is still totally unknown.
What if it's the other way around? (Score:2)
Man Gets 70mpg in Homemade Car-Made from a Mainframe Computer [xnewswire.com]
Re:What if it's the other way around? (Score:4, Interesting)
Wouldn't that be like the researcher who, several years ago, proposed the theory that The Odyssey was not written by Homer the blind poet but was in fact written by a completely different blind poet named Homer?
Re:What if it's the other way around? (Score:2)
But it sure could be.
This Just In ... (Score:4, Funny)
Re:This Just In ... (Score:2)
Not really full of stars ... (Score:2)
Re:This Just In ... (Score:2)
How Really is Really? (Score:2)
Ten Thousand Things (Score:2)
oops (Score:2, Funny)
They later recanted their findings saying that the donut-shaped ring was really just mold growing in the telescope from three seasons of constant rain.
Not quite a ring... (Score:3, Informative)
Ring of Stars, Johnny Cash version (Score:3, Funny)
And it made a fiery ring
Well beyond spirals and bars
It fell into a ring of stars.
And it burns burns burns, oh the ring of stars
It turns round round round out where matter's pretty sparse
And it burns burns burns, the ring of stars
The ring of stars.
In Other News (Score:3, Funny)
When asked to comment, an onlooker suggested: "Maybe they're just really hungry?".
Occam speaks (Score:2)
Re:Occam speaks (Score:2, Insightful)
From the article: The ring appears to be about 10 times thicker than the disk, Yanny said.
This thickness implies that the ring of stars would not be just an outer galactic arm -- galactic arms are composed of young stars, formed out of gas very near the galactic midplane. Stars can compose a thickened disk, but gas cannot, as if two parcels of gas on inclined orbits collide with one another they each have their inclinations reduced. Stars however, pass right through one another.
There is another population of stars in the main part of the galaxy that is 'thicker' than the main population and is composed entirely of old, small, red stars that are the result of a 13 billion year old galaxy collision.
Re:Occam speaks (Score:2)
Has a similar ring been observed around any other galaxy? If not, why do we jump the the conclusion that what we are seeing is new and different when simpler explanations are in front of our face?
And I thought we had it bad... (Score:5, Interesting)
There's a novel by Iain M. Banks called "Against A Dark Background" that deals with this (the book may or may not be a part of his Culture universe), a space faring civilization arises in a solar system far outside of a galaxy. They expand outwards to colonize all available planets in the system, then, despite sometimes attaining staggering technological advances they stagnate. The utter isolation of their situation sinks in, unable to expand any further they eventually decline - sometimes almost back to medieval levels, only to eventually progress back to the point of space travel and the cycle begins again...
Re:And I thought we had it bad... (Score:2, Interesting)
the only reason we find it difficult to entertain the idea of visiting stars many (like, say, 30,000) lightyears away is because the human lifespan is so damn short.
There are two ways around this problem.
1) find ways of travelling really fast (i.e. >c, via whatever dreamy technology / worm-hole / whatever), or
2) make sure each human conscious can survive a good million years (or indefinitely, for good measure), cybernetically or otherwise. A trip to the end of the galaxy and back would be like a two-year backpacking trip to europe in our current life-span-terms.
of course, this would make one helluva different perspective shift, (as civilizations rises and falls within spans of centuries)... It would certainly re-define "macro" and "micro," which would be kind of fun.
Re:And I thought we had it bad... (Score:2)
Fortunately you can save your pity, as there likely isn't much (if any) life on stars near the edge of our galaxy.
The latest postulation in this "science" is that the inner 1/3 of our galaxy and the outer 1/3 would be barren. The inside would be dead because the cosmic radiation from such a dense mass of stars would be devastatingly hostile to any developing life forms. The outside would be lifeless because there wouldn't be enough supernovas to create sufficient quantities of useful elements (stuff besides H and HE).
Of course, that leaves a third of the Milky Way, which is still a hell of a lot of stars.
oh, I know what it is (Score:2, Funny)
more data needed (Score:2, Insightful)
However, one could speculate that if these stars are indeed part of a ring, the ring may have formed through a collision with another galaxy. For an example, check this [hubblesite.org] out. Here [hubblesite.org] is another example of a ring galaxy.
Big Bang Nucleosynthesis (Score:3, Insightful)
Not the Dark Matter. (Score:2)
The second problem is that there must be a LOT of DM.. Not a few faint stars..
Re:Not the Dark Matter. (Score:2, Interesting)
I can't help but think something like this, in combination with the theory that black holes in one universe are the points of origin for adjacent universes. I've heard it said before that most galaxies have a black hole at the center at the least?
That might account for both of your points, along with the observation that the universe is constantly expanding (matter continuously arriving through the black hole in another universe).
Re:Not the Dark Matter. (Score:3, Interesting)
Many people do not realise that general relativity equation do have some fairly heavy assumptions - like requirement for the equations to be of no higher then second order. It may be possible to write a different theory that will lead to non-linear beahviour of acceleration for small forces. That would explain rotational curves (the most solid evidence for dark matter) without dark matter.
Nevertheless, WIMPs involve less new assumptions, at elast at this moment, so Brother Occam tells us it must be true..
The Milky Way is a Barred Spiral (Score:2, Interesting)
That explains it. (Score:2)
Wow, that explains why he made the international sign of the donut [sciflicks.com].
LOTR? (Score:2)
In Soviet Russia... (Score:2)
Speculation (Score:2)
I have an idea that I've never really read anywhere, and I've always wondered why. What if gravity is a source of both attraction and repulsion, but the attraction affect is much stronger within a certain locus, such as within a galaxy? Now, take that idea and imagine a sort of fractal effect, leading to clusters of galaxies, and clusters of clusters.
So the affect that pushes galaxies away from each other is also gravity, but Newton's law gets bent over intergalactic distances.
I'm stepping all over everyone's toes here, because I've had only basic physics coursework, so I apologize now to any astrophysicists I might have offended.
Those are not stars! (Score:2)
Re:Only 1%? (Score:2)
Re:short answer (Score:4, Funny)
Yes.
Hey look at me, I provided an answer with absolutely no evidence to back it up, gimme a +1 informative!!
Re:short answer (Score:4, Funny)
I was wondering who was talking about dark matter so much lately, and it was you two! Problem solved.
Re:short answer (Score:4, Funny)
Re:short answer (Score:4, Interesting)
Yes.
Most scientists believe that dark matter makes up 80 - 95% of the total gravitational mass of the galaxy, and probably the universe.
Dark matter is simply the term given to matter that we haven't observed yet, except indirectly through its gravitational effect.
This is certainly some portion of the dark matter. But I wouldn't say a significant part, or even a part really worth mentioning. While the dark matter is almost definitely comprised of several different sources, it seems certain to me that there is an entire class of gravitational objects that we have yet to observe, and this is the cause of the dark matter. Whether its dark stars, black holes, heavy neutrinos, or some even more strange and cosmic form of matter I don't know. It could be all of those and more.
Point being, if the dark matter within the Milky Way is only 80% of the mass of the galaxy, and not say 95% as some researchers suggest... this would make it 400% of the mass of the observed portion of the galaxy. These stars are, according to the article, 1% of the mass of the (previously) observed portion of the galaxy. Which makes them 0.25% of the mass of dark matter required to account for gravitational effects that are otherwise unexplained. If dark matter turns out to be a significantly larger percentage, such as 95%, then these stars only account for
For those who question the value of determining either the cause or the exact amount of dark matter in the universe, this debate is pivotal for determining the final fate of the universe. So far our calculations of the total mass of the universe, including the dark matter, are riding the knife-edge required to make the universe exactly stable. If there is a little more mass than this, then the current expansion of the universe will one day reverse, until the universe contracts back to a singularity. If there is a little less mass than this, then the current expansion of the universe will continue infinitely.
This is all according to current theory on the creation and eventual fate of the universe and is subject to change with brilliance, genius, and persperation.
Re:short answer (Score:2)
>Yes.
I vote no. Stars are luminous and dark matter is not luminous by definition. This could be said to be part of the "missing matter", but not the "dark matter". Argumentum ad lexicon, QED.
Anyway, isn't dark matter supposed to be a hypothesized explanation for why stars in spiral arms are orbiting the centers of galaxies more quickly than can be accounted for by the observed abundance of luminous matter? I'm not familiar with the gravitational properties of a ring-shaped mass distribution, but a ring of stars surrounding the outer rim of the galaxy seems to be in the wrong place to have any explanatory power for the high orbit velocities of stars that are well within the ring. You want to find something heavy that's within their orbits.
Re:short answer (Score:2, Informative)
No, because dark matter is thought to be the explanation for galaxies moving apart faster than conventional explanations, so dark matter is assumed to exist and cause a negative gravitional attraction (negative mass, not anti-matter), to explain observed behavior.
Even if you assume postive vs. negative matter is not the issue, the ring around the galaxy is much to small in mass to make much of a difference anyway (much smaller that assumed dark-matter).
Re:short answer (Score:2, Informative)
Dark matter is the [largely] undetectable matter that is proposed to contain a significant portion of the mass of the universe; the mass which is unaccounted for by visible matter. There are three main [current] theories about this:
MACHOs. I forget what the acronym stands for, but these are essentially hugely massive particles which are still small. As such, they account for a significant amount of mass without occupying much volume in space. This lack of significant volume (and their relative seperation) makes them difficult to detect.
WIMPs. This acronym was chosen to compete with MACHOs, actually, in a fit of playfullness by scientists. It stands for Weakly Interacting Massive Particles. These are actually quite similar to machos, but are formulated differently mathematically.
Massive neutrinos. Without getting too much into theory, there are many types of neutrinos. If some of them are at all massive (and current experiments suggests that they are) then their massive numbers could account for a significant amount of the missing mass.
Re:dark matter (Score:2)
Re:So when is it not part of galaxy? (Score:4, Informative)
Re:So when is it not part of galaxy? (Score:2, Insightful)
I would venture that the distinctions between different classes of gravitationally bound clusters of stars (star clusters, galaxies, galaxy clusters..) are fuzzer in practice than on paper. After all, the Universe is a dynamic place.
Re:No, no dark matter. (Score:2)
Re:Is it just me.... (Score:2)