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Galaxy Sans Dark Matter
ChromaticDragon writes "Astronomers have crunched some numbers on a galaxy to discover that its rotation can be fully explained by the gravity of the observable matter — in effect, this galaxy seems to lack dark matter. This shouldn't come as a total surprise given that one of the stronger observations of Dark Matter was the
Bullet Cluster where supposedly a good deal of Dark Matter and good old fashion regular matter had separated."
Yeah.. guess what guys! We just discovered this awesome stuff called Dark Matter! Really? Yeah... Can we see it? um.... it doesn't exist in this galaxy.
Excuse me while I gather the virgin sacrifice and assemble the pentagram required to solve your problem
I'm not sure if it is the story the submitter was trying to link to, but this article seems to cover the subject.
I thought that was supposed to be a joke... would have been much more effective if it immediately shutdown your computer when you clicked it though...
Black Matter [Click Here]
Black Screen...
All the Dark Matter is there, it just was told to move to the back of the galaxy.
Learning HOW to think is more important than learning WHAT to think.
No (or negligible) dark matter in our galaxy, eh?
When we're looking farther away, we're looking back in time, too. So perhaps the observations could be explained by "constants" of physics (notably the gravitational constant) varying with the age of the universe, rather than by the gravitational pull of some otherwise-unobservable dark matter.
Let's see if "dark matter" is "more dense" the farther away we look... B-)
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
This is really interesting after reading a recent /. story about dark matter, and getting some more information from another poster. If dark matter was needed to explain why galaxies look a certain way, but this one can exist without it, what does that say about dark matter? Even if dark matter is real, there's obviously something missing if we can't explain this.
Nature, you have once again awed me with your incredible weirdness.
This is another nail in the "dark matter can be solved with a modified theory of gravity" coffin. If we can find a galaxy composed of stars whose observed motion is entirely explained by the mass of those stars and known theories of gravity (Newton, Einstein) that's a serious blow to theories like MOND.
Killing two birds with one stone - dark matter decays to dark energy, with a half-life of (multiple millions of years here).
Im with the string theory people and what we are seeing is an "effect" of multidimensional space.
Broken link? I don't think so..
It says 404.. Not Found.. Pretty much in line with TFS...
'Let's see if "dark matter" is "more dense"' I dunno, usually blond matter is more dense...
Excuse me, but please get off my Pennisetum Clandestinum, eh!
That’d be more like “serious suck,” wouldn’t it?
Er... & isn’t MOND just like MONO only it O-D’ed?
I suspect that all of the dark matter is still there, it’s just much better adapted to the background than the Caucasian matter. Happens often with some Zambian flatmates & myself.
Got time? Spend some of it coding or testing
Umm, no.
There are some good reasons to believe it isn't normal matter that isn't making light. For starters one would still expect it to absorb light and thus be observable. Additionally our models of galaxy formation would suggest it should have a certain distribution which doesn't conform with what is necessery to explain the rotation behavior. In fact it may even need to be relatively free from interactions to be as spread out as needed. Most relevantly the observations that suggest that dark matter doesn't collide with itself or normal gas when galaxies collide suggests it isn't normal matter.
Of course your general sentiment is right. There are reasons to believe dark matter isn't made up of neutrinos but it isn't any more mysterious than they are. It is probably just some weakly interacting particle much like those we have already discovered.
If you liked this thought maybe you would find my blog nice too:
Not only can you not see the dark matter (and it appears to be devoid), but now, you can not find the link to it.
I prefer the "u" in honour as it seems to be missing these days.
OK, it's now more than twenty years since my astrophysics degree, but the fundamental principle of cosmology was that, at a large scale, the universe looks the same everywhere. Now we are being told it does not and, in fact, we live in a special corner?
No Reapers in the Milky Way, then.
It's just a way for the editors to abrogate their responsibilities while blaming the users when crappy submissions get posted.
I thought I could contribute a bit to the discussion by giving some background on why the theory of dark matter came about.
Vera Rubin's work on galaxy rotation rates is still pretty compelling evidence for dark matter... OR, at least, it shows us that all galaxies do not behave they way we think they should, to be more accurate. People much smarter than my own self have decided that "dark matter" or some sort of mass/force/something that does not emit light or radio waves, etc. (which is why we never noticed it before) must be responsible.
When we look at a solar system like ours, we see that the farther a planet is from the sun, the slower it travels. Not only does it have a much longer way to go, but it doesn't - and according to what we understand, shouldn't - travel as fast.
Vera Rubins decided to check a whole galaxy. What she found did not hold with our understanding. The solar systems, stars and other observable matter near the outside were traveling faster than expected.
Vera Rubin's work, combined with the discovery that the univers appears to be expanding at an accelerating rate, rather than slowing down, kind of kicked off the whole dark matter/dark energy thing.
Well, my days of not taking you seriously are certainly coming to a middle. -Firefly
at the going rate, we probably have this all wrong, and its either ridiculously simple, or so insanely much more complicated that we're going to have a collective infarction when we finally get a grasp on how it really works.
I've decided to Diversify my Holdings. I've divided my cash between my left and right pockets, instead of all in one.
If the universe was full of life what would it look like? Just roll the idea around for a while. Look at what current SF writers are thinking about, that we may soon be starting on our own primitive Dyson Sphereshttp://en.wikipedia.org/wiki/Dyson_sphere. That we may eventually use all the energy from our sun and give of no visible radiation. It might seems impossible now but imagine we are going to work on the problem for a million years. If the universe was full of intelligence, I think it would look just like what we see now.
There have been a couple of observations that suggested that in galactic colisions or near colisions, that the dark matter can go on, and the visible matter can change course. Visible matter reacts with the gas streams, the dark matter doesn't seem to. I saw a report a couple of weeks ago of a dark matter galactic halo without a galaxy. (Found by the Einstein lensing effect.) We now have a galaxy without a dark matter halo. Looks like we have all the pieces of the puzzle, now someone just needs to put them together. That'll make a nice Doctoral Thesis.
Mond will be a casulty though. Well, that's how science progresses. the only thing certain is that the theories we have today will change.
Everybody knows 3 people with my name.
I thought WIMPs (weakly-interacting massive particles) and MACHOs (whatever) had been essentially ruled out by exclusion in various experiments. That leaves a new form of non-baronic matter that doesn't interact with itself, baronic matter or light except through gravity.
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
Let's not forget Occam's Razor. Complicated theories are usually a precursor to more elegant ones.
It's not some magical, physics breaking, mysterious subject. It's matter with no light shining on it.
Apart from the fact that dark matter in galaxies is distributed as a spherical halo whereas the normal matter is distrubuted as a disk the after glow of the Big Bang shows that dark matter is not normal, atomic matter.
The WMAP probe measured the temperature variations of the huge cloud of plasma that was the entire universe for the first 380,000 years after the Big Bang. The problem is that for temperature variations the plasma must have had different densities this means that something must have been causing the plasma to clump (plasma is like water: if you try to compress it at a point and then remove the compression force the particles bounce off each other and form waves so no more clumping).
Ok so far? Well to make the clumps we need gravity so the problem now is what compressed the plasma? If cannot have had an electric charge because then it would get bound up with the charges in the plasma and act as part of the plasma (EM forces are a lot stronger than gravity). Hence it much be neutral. If we look at all the stable particles we know of only one type of particle fits the bill: the neutrino.
Unfortunately the neutrinos are very light and rarely interact with anything (you would need light years thickness of material to stop them!). The result of this is that they are produced early on in the Big Bang when the density was very high but when the energies were also very high. This means that they are very fast moving particles. So if we had a "clump" of neutrinos they would quickly move apart and spread the clump out. The problem is that the size of the clumps in the WMAP picture are far too small to be explained by neutrinos.
So, the result of this is that we need a massive, neutral particle that is slow moving....and we don't have any. Hence the need for something new. The question is whether this new particle will interact just through gravity or through both gravity and the weak force. The latter will mean we can produce and detect it in particle accelerators if we have enough energy but the former will mean that it will likely remain out of reach for the foreseeable future.
Perhaps dark matter is "simply" right handed neutrinos -- which by virtue of their relationship to the light, left handed neutrinos would be massive -- and hence currently "cold"?
A puzzle:
Since matter with no electric charge can not form "atoms" -- and matter with no quark charge can not form "nucleons" , there is nothing to stop a concentration of dark matter, say, the mass of a star, from gravitationally collapsing very quickly to a rotating, uncharged black hole.
And once dark matter is safely quarantined in a black hole it can interact with matter -- including dark matter quite readily.
So, why isn't the galaxy riddled with black hole "trails" through interstellar gas like electron trails through a cloud chamber?
A 2 for 1 Solution:
Perhaps in the very early universe most of the dark matter quickly formed micro black holes -- most of which evaporated via Hawking radiation -- and perhaps that radiation pressure is what is driving the more rapid expansion of the early universe attributed to "dark" energy?
SO, perhaps the "missing mass" dark matter in most galaxies is "just" micro-black holes that haven't yet evaporated and free right handed neutrinos ?
Perhaps NGC 4736 is simply in a region of space-time where most of the early right hand neutrinos formed primordial black holes that have mostly evaporated?
The universe. Damn queer place.