The shroud of the darkside has fallen…
Yoda
Astronomers have used data from the Hubble Space Telescope to construct a "map" of "dark matter" around a galaxy cluster, as reported in the June 1 issue of the Astrophysical Journal. All matter has gravity, and so far about the only evidence found for dark matter is in the subtle gravitational effects it has. Dark matter goes unseen because it is too widely spread through the Universe, is made up of particles too small to reasonably detect, or is too cold to emit enough electromagnetic radiation (light). Many astronomers consider it to be ordinary ("baryonic") matter made of atoms like everything you encounter everyday (including yourself). It could also be some new and exotic, as yet undiscovered type of matter ("non-baryonic"). No one knows.
For some time, dark matter has been considered a key ingredient in determining the fate of the Universe. Basically, if there is enough mass in the universe, then you can say [somewhat incorrectly but OK for now] that it is heavy, and can fall down as an apple can fall from tree. Except in this case the Universe would collapse down on itself, possibly turning the Big Bang into a "Big Crunch." Given just the amount of matter that we can see and account for directly, there is nowhere near enough.
If there is not enough dark matter, you can say that the Universe is light and will expand outward forever. The problem is that evidence for dark matter has always been circumstantial, based in large measure on the rate at which galaxies and galaxy clusters rotate. If you tally up the number of stars and gas clouds in a galaxy like the Milky Way, you can calculate through the laws of orbital mechanics, at what rate it should rotate. However, in most every case, astronomers find that galaxies and clusters rotate much faster than expected, and the only good explanation is that they are more massive than they appear. But where does this extra mass come from? The suggestion for years has been dark matter, but has been just a suggestion because no one could actually see any of it. Now it appears that we have good, more-or-less direct, evidence of a ring of dark matter around the galaxy cluster ZwCl0024+1652.
Theoretical considerations point to 10 to 100 times more dark matter than regular matter. But even with the circumstantial evidence through rotation rates and gravitational effects on the light from distant galaxies, astronomers can’t account for much of it.
It seems likely that we now have new and more direct evidence that dark matter actually exists, astronomers still don’t know for sure how much there is. And in the long term it may not be that important, anyway, because several years ago other astronomers a curious phenomenon now known as "dark energy." This appears to speed up the expansion of the Universe, such that much more dark matter than anyone expects would be needed to stop the expansion. So the current observational evidence suggests that the Universe will expand forever into cold nothingness. But who knows? We’ll just have to wait and see. Stay tuned, but don’t hold your breath!
Credit: NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University), Hubblesite.org
Larry, this is very interesting. I wondered when I read your post how they discovered this ring, but when I followed one of your links I saw that they saw it in visible light. Is that correct? I’m hoping I understood what was being said, in a quick read.
Here’s a quote from the article, which is here.
“This Hubble composite image [the image in your post] shows the ring of dark matter in the galaxy cluster Cl 0024 17. The ring-like structure is evident in the blue map of the cluster’s dark matter distribution. The map was derived from Hubble observations of how the gravity of the cluster Cl 0024 17 distorts the light of more distant galaxies, an optical illusion called gravitational lensing. Although astronomers cannot see dark matter, they can infer its existence by mapping the distorted shapes of the background galaxies.”
Visible light? That’s wild! I wonder if you could see it if you were close enough to it in space …
Deborah
I hope I am still around when they finally find out what “black matter” & “black energy” turn out to be.
My understanding is that it is visible light data, but I didn’t think it was a photo per se. Hence the word “map”. As I interpret it, the image that they show is a visible light photo of the galaxy cluster, but the bluish cloudy ring representing the dark matter is superimposed data not actually in the image. As the excerpt says, they have looked at the distortions in the images of some of the galaxies, due to the “gravitational lensing,” and have calculated the distribution and density of the unseen matter that would be needed to cause those distortions. So it is a bit misleading to imply that they actually saw the dark matter, as I understand it.
Depending on exactly what dark matter is, I supposed that some dark matter could be visible if you were close enough and under the right lighting conditions. But most likely the majority of it is so widely dispersed in space that it just can’t be seen by the human eye. Very few of the images we see from the Hubble or other large scopes would appear anywhere near as spectacular to the human eye, even if we were “up close,” just be cause they are time exposures that let the image build in a way that our eyes can’t.
You said baryonic matter is made of atoms, so I assume that baryonic includes solid, liquid, gas or plasma. This seems like an entirely new type of matter which may make it’s own category. This is a very interesting and mysterious topic and I look forward to seeing breakthroughs in the research on dark matter.
actually, larry, that would be very interesting to know. is this in fact an artist’s rendering based on map data? that seems likely, but it makes this picture (or the article, really) a bit trickier to interpret.
Sglasson and Beth:
Baryons are subatomic particles made up of smaller particles called quarks. Primarily they are protons and neutrons, which along with electrons, make up all normal atoms in the Universe. Electrons themselves are non-baryonic, and they are much less massive than the protons and neutrons. Another type of non-baryonic particle is called the neutrino, which have very little mass (individually) and are extremely hard to detect. While it seems unlikely that there are other stable and numerous baryon types other than the ones we already know, there could be other types of non-baryonic particles, and perhaps even forms of matter with properties markedly different from what we know.
As far as the picture goes, my understanding is that the galaxy images are real, but that the cloudy ring has been added and is just a representation of where the dark matter is, not an actual image of it. I’d have to check this further, but that is my understanding.
LS
Dark matter doesn’t exist people. Even most scientist out there will tell you this. This is our way of trying to save ourselves from the reality that we really don’t know anything. They know that if they can’t say that something like this exist then the law of gravity that they stand on so much and have taught all of us can’t be true. So instead of facing this fact that we can’t and never will know how all this really works they make up a term and a substance like this. Something you can’t prove doesn’t exist and say that it does. Well, I’ve got a better reason why the universe expands and why we have gravity. It’s because of Water on Earth and as long as water exist gravity will continue to work and the universe will continue to expand. Now prove me wrong….when the planet runs out of water( dumb right…well so is Dark Matter)
Dear What What?
There’s an old saying: “If it walks like a duck, and sounds like a duck…” well, you know the rest. Dark matter is really more than a theory — it is a reasonable explanation for observed phenomenon based on what we know about physics. In the long run, we may find that there really isn’t enough dark matter [although we know for certain that some exists, such as vast amounts of neutrinos formed in every star] and that some other as yet undiscovered phenomenon can account for the effects we see. Ultimately, you are right that we really “know” nothing. I don’t “know” that you aren’t an alien from the planet Zipfast, nor do I really even know you exist. It might just be my mind playing tricks on me. The only way to truly know anything is to know everything — to omniscient, which by some definitions would make us God. Personally I don’t qualify and I doubt that you do either, so neither of us [or just me, if you aren't really there] can claim to know anything in an ultimate sense.
But that does not mean that we should take the negative attitude that we our basic science is wrong. Ptolemy’s “cycles and epicycles” model of the Universe was a flawed though reasonable idea in its time, but has since been shown to be wrong. Newton’s gravity works admirably well to describe the motion of falling bodies and for the most part spacecraft traveling through space, but we know that ultimately it is only a mathematical approximation. A basic tenet of quantum physics has long been that we may never know ultimate answers, but that we should still use what we do know — or at least what works — to find out more.
Putting forth hypotheses such as Fritz Zwicky and Vera Rubin did with the original ideas of dark matter takes mental courage, intellectual integrity and solid reasoning. It is the way that good science works.
Dark matter surely exists since there are known particles that qualify — as well as larger objects such as small stars or planets yet to be discovered. We can’t see stars in many distant galaxies even with our largest telescopes, but it is unreasonable to say that they don’t exist. We have good reasons other than direct observation, including several lines of indirect evidence and analogy to known situations (the Milky Way and other nearby galaxies).
So the real questions — the honest and reasonable questions — is not whether “dark matter” exists, but how much of it is there and does it fully explain the observed effects? If we get hung up on the need to know everything with absolute certainty, there would never be any progress in science or anything else.
quantum mechanics predicts dark matter and expansion,it also predicts that matter is popping in and out of existance.do you think it is possible that as expansion speeds up so will the appearance of more matter resulting in a slow down of expansion? sort of a pendulum effect.
Sam,
I’m not sure that quantum mechanics “predicts” either dark matter or the expansion, except maybe in the broadest terms. Certainly the Big Bang and the existence of matter could be a consequence of quantum effects. As for whether a speed up in expansion is followed by an increase in matter, I don’t think so. There is no evidence of that nor as far as I am aware, any good reason to think it so. However, your idea is in fact a basic tenet of the old theory called “The Steady State” Universe, in which new matter was created to just balance the expansion rate. But while there is precious little evidence to support the Steady State, and strong evidence (e.g., the Cosmic Background Radiation) to refute it, there is no direct evidence against the idea that new matter can be created spontaneously in the Universe. Although quantum effects may be the “cause” of the Universe in the beginning, the constant creation of “virtual” particles does not result in any wholesale production of matter, because within an incredibly short period of time after a virtual particle is produced through quantum effects, it pops back “out” of existence, leaving the total mass of the Universe unchanged. At least that is the way it works in our neck of the woods, and everywhere else we can check. We have no evidence of it. But it would be foolish to say that spontaneous creation of matter is impossible because we don’t know the mechanism. Still, until we have physical evidence supporting the idea, and a reasonable mechanism to explain it, it doesn’t seem likely.