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Ring Of Stars Found Around Milky Way
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?"
Could this be part of the elusive 'dark matter' talked about so much lately?
no
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 for more information.
Nobody knows what dark matter is yet, but there are lots of guesses.
Somewhat offtopic:
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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.
Isn't dark matter simply matter that doesn't emit light? If stars get formed by huge clouds of gas that eventually create so much heat and pressure that it starts a process of fusion, then its more than likely all this dark matter we are talking about is just that, dark matter, dirt, whatever you want to call it.
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.
your concept of dark matter is incorrect. dirt is not dark matter. it emits black body radiation. I believe you are also confusing "radioactive" with "radiative".
Dark matter must either be some strange particle, or must be a change in the laws of gravatation (the latter is considered not likely).
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).
-pyrrho
Dark matter is just the term for matter that we can't detect. It can be baryonic material or even black holes. "Dark" doesn't mean 'invisible' when they use it in that context.
No, some matter could (according to both relativity and quantum physics, not to mention string physics) have not only negative energy (and thus negative mass), but also travel through different dimensions in different directions.
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).
"Stumble before you crawl"
Sounds like they've discovered a Kemplerer Rosette [burtleburtle.net]. :)
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.
I am disrespectful to dirt! Can you see that I am serious?!
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.
visit the hwky website for a lyrical genius infusion.
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 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 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! :)
In the August 2002 edition of Scientific American, an alternative to Dark Matter is explored in the cover article. This alternative, called Modified Newtonian Dynamics (MOND), basically (VERY basically) proposes that F != ma, and that there is a very slight exponential component to the curve at extremely low accellerations, such as is experienced by large galaxies interacting. At more "traditional" accelerations, the curves become virtually identical, and MOND behaves almost exactly like the classical equation governing motion.
A gateway to some knowledge about this topic is at The MOND Pages . I'm sure if people search around, they can find better sources, but it remains an interesting topic to discuss in relation to the "missing matter" problem. If this pans out, then maybe not much is really missing at all. Or maybe a lot is. Only time will tell which theory is correct.
Erioll
Dark matter is just the term for matter that we can't detect. It can be baryonic material or even black holes. "Dark" doesn't mean 'invisible' when they use it in that context.
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 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".
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- - You can't take something off the Internet! That's like trying to take pee out of a swimming pool.
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.
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That's essentially it, yes.
:)
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.